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Trends in rates of chronic obstructive respiratory conditions among US military personnel, 2001-2013.

Chronic obstructive pulmonary diseases are a group of respiratory conditions characterized by difficulty breathing, airflow limitation, and symptoms that include cough, wheeze, and sputum production. This category of conditions includes bronchitis, not specified as acute or chronic, chronic bronchitis, emphysema, asthma, bronchiectasis, extrinsic allergic alveolitis, and chronic airways obstruction, not elsewhere classified. Asthma is a chronic inflammatory condition of the lungs characterized by intermittent, reversible airway obstruction. The prevalence of asthma is 8.2% in the general adult population of the United States. (1) Emphysema and chronic bronchitis are often associated with a history of cigarette smoking, and characterized by fixed, irreversible airway obstruction. In 2011, the prevalence of chronic obstructive pulmonary disease (COPD) (emphysema and chronic bronchitis combined) was approximately 6% in the US adult population. (2) The prevalence of COPD increases with age, rising from 3.2% among those aged 18 to 44 years to more than 11.6% among those 65 years old and older. Together, chronic lower respiratory diseases constituted the third leading cause of death in the United States in 2008, although deaths from chronic lung disease occur primarily after age 65. (3)

In 2011, respiratory diseases were responsible for over 250,000 medical encounters among active duty US military personnel, excluding respiratory infections. (4) Although the burden of respiratory disease among the military is dwarfed by those imposed by injuries, mental disorders, and musculoskeletal diseases, respiratory conditions can be debilitating and sufferers' lives can be severely affected. Trends in respiratory health have implications for force readiness, allocation of military healthcare resources, and Veterans' care.

In October 2001, the US military initiated combat operations in Southwest Asia. More than a decade later, many of the impacts of prolonged military engagement on injuries, mental health, and behavioral disorders among military personnel have been well documented. (5-11) The potential effect of deployment-associated environmental exposures on lung health is also of concern, (12) but associations between military deployment and incidence of chronic obstructive lung conditions are not as well characterized. Some studies have reported associations between pulmonary health status and deployment, (13-17) while others have not. (18,19)

Changes in the respiratory health of the US military population over time may result from variation in the demographic profile of the population, trends in accession standards, deployment-associated and other environmental exposures, and trends in smoking behaviors.

The purpose of this surveillance effort was to estimate and evaluate longitudinal trends in rates of chronic respiratory conditions in the active duty US military population from 2001 through 2013, and answer the following questions:

1. What are the rates of these conditions in the military population?

2. Have the rates changed over the past 13 years?

3. Do the rates, and particularly the trends in these rates, vary by branch of military service, job category, or rank?

METHODS

Study Population

The study population consists of active duty personnel serving in the Army, Air Force, Navy, Marine Corps, or Coast Guard, and served by Tricare * at any point during the period January 2001 through December 2013.

Ascertainment of Respiratory Diagnoses

Incidence rates (2001-2013) of chronic obstructive pulmonary diseases among US military personnel during the period 2001 through 2003 were estimated using diagnostic records for ambulatory medical encounters maintained in the Defense Medical Surveillance System (DMSS). Records for medical encounters within the military health system and doctor visits in the private sector that were paid for by Tricare are included in DMSS. Annual rates for the conditions of interest were calculated by dividing the total number of cases by the total person-years at risk during the year.

Definition of Respiratory Diagnoses

Trends in annual incidence rates were assessed for each subclassification in the broad International Classification of Diseases, Clinical Modification (ICD-9) category of COPD and allied conditions (ICD-9 codes 490-496). Case status was defined using 3 increasingly specific rules: The primary definition required there to be at least 2 ambulatory medical encounters recorded in DMSS with identical ICD-9 codes within 2 years (730 days). For example, to qualify as an asthma case using this definition, personnel were required to have a minimum of 2 outpatient encounters coded with ICD-9 493 within 730 days. The second, more sensitive case definition required the appearance of only a single ambulatory medical encounter with a given ICD-9 code. The third, more specific case definition required there to be at least 3 ambulatory medical encounters with identical ICD-9 codes within 2 years. In all cases, the date of the first medical encounter with the corresponding qualifying ICD-9 code was defined as the date of incidence for the purpose of person-time calculation. Individuals with a given diagnosis prior to 2001 were excluded from the analysis. Cases identified in a given year were excluded from the person-time and rate calculations for subsequent years.

Statistical Analysis

We analyzed anonymized ambulatory encounter diagnoses data that had been aggregated by year. The data were received for the entire population and stratified by rank (junior enlisted (E1-E3), senior enlisted (E4-E6), junior officer (O1-O3), senior officer (O4-O6)) and branch of military service (Army, Air Force, Navy, Marine Corps, Coast Guard). Trends in rates and natural log-transformed annual rates over time were assessed using linear regression analyses. Assessment of curvilinear relationships between medical encounter rates and year were assessed by including a quadratic term for year ([year.sup.2]) in the models.

Differences in annual rates and the time trends of those rates were evaluated by branch of military service, military job category (combat, healthcare, other), and category of military rank.

To assess whether time trends differed by branch of military service, models were constructed to include main effects for year of diagnosis and indicator variables for each branch of service, as well as interaction terms defined as the product of year of diagnosis and each indicator variable. The Army was used as the reference group for analyses of service-specific trends. Noncombat roles were the reference group for military occupation, and junior enlisted personnel served as the reference group for categories of military rank.

All statistical analyses were conducted using SAS 9.2 (SAS Institute Inc, Cary, NC). The trends over time are presented using the primary case definition. Differences in the estimated average rates for each respiratory diagnosis using the more strict case definitions are also presented.

The Public Health Review Board of the US Army Public Health Command reviewed and approved this evaluation.

RESULTS

Demographic Summary

A summary of demographic and mil itary characteristics of the study population is presented in Table 1. The military population at risk of respiratory health conditions in this study included 3,800,676 individuals and over 18.1 million person-years of observation. The majority of the study population were male (84%) and of white, non-Hispanic race/ethnicity (64%). Army personnel comprised 38% of the study population. Almost half of the population (47 %) was aged between 20 and 24 years.

We obtained diagnosis codes for the broad category of COPD and allied conditions (ICD-9 490-496) corresponding to 482,670 ambulatory medical encounters occurring during the 13-year time period from January, 2001 through September, 2013. Of these, more than half (57%) were encounters for bronchitis, not specified as acute or chronic (ICD-9 490) and more than a third (37%) were for asthma (ICD-9 493) (Table 2). Requiring 2 ambulatory visits with the same diagnosis within 2 years to qualify as an incident case results in a total of 156,516 personnel with a chronic obstructive lung condition. Requiring 3 ambulatory visits with the same diagnosis within 2 years further reduces the total number to 81,843 incident cases. Seventy-eight percent of the cases for this last, most restrictive case definition were for asthma, and almost 18% were for bronchitis, not specified as acute or chronic.

Rates of Bronchitis, Not Specified as Acute or Chronic (ICD-9 490)

Over the 13-year study, 276,878 ambulatory medical encounters for "bronchitis, not specified as acute or chronic" (ICD-9 490) occurred among active duty US military personnel, yielding an average rate for this nonspecific diagnosis of 27.7 cases per 10,000 person-years (95% CI: 21.4-35.9) over the study period using the primary case definition requiring at least 2 visits in 2 years (Table 3). Relaxing the requirement for there to be at least 2 ambulatory encounters coded with ICD-9 490 within 2 years results in a dramatic increase in the estimated average rate (144.3 cases per 10,000 person-years; 95% CI: 122.9-169.5). Requiring at least 3 encounters within 2 years to define case status resulted in a correspondingly dramatic lowering of the estimated rate of bronchitis not specified as acute or chronic to 7.0 cases per 10,000 person-years (95% CI: 5.1-9.5).

Branch of military service was a statistically significant predictor of the rate of bronchitis not specified as acute or chronic, independent of the year of diagnosis. Army personnel had significantly higher rates relative to all other branches of military service except for Marine Corps personnel, although the differences were only statistically significant in comparison to Navy (P = .0017) and Air Force (P = .0425) personnel. Marines had a higher average rate of bronchitis, not specified as acute or chronic, relative to Army personnel (P = .0425). Rates were lower among those with military occupation classified as combat, relative to those in noncombat occupations (P < .0001). Rates of bronchitis, not specified as acute or chronic, were also lowest among junior enlisted personnel relative to senior enlisted personnel and officers (P < .0001).

The temporal trend in rates for this nonspecific bronchitis diagnosis followed a [intersection]-shaped curve ([P.sub.quadratic year term] = .0003) (Table 4). Rates increased by an average of 17 cases per 10,000 person-years per year from 20012009 (P < .0001), then decreased by almost 24 cases per 10,000 person-years per year from 2009-2013 (P = .0175) (Figure 1). By 2013, the rate (15 cases per 10,000 person-years) returned to levels similar to those observed in 2001 (17 cases per 10,000 person-years). Notably, both the increase prior to 2010 and the subsequent decrease in the rates of this diagnosis were much more pronounced for Marines than personnel in any other branch of military service.

Although the magnitudes of the rates differed, the [intersection]-shaped pattern of the trend in rates were consistent, albeit more pronounced when using the more sensitive case definition ([P.sub.quadratic year term] = .0002), and almost identical when using the more specific definition requiring 3 or more ambulatory encounters within 2 years ([P.sub.quadratic year term] = .0020) with diagnoses of bronchitis, not specified as acute or chronic.

Significant statistical interactions were not observed between year and branch of service ([P.sub.interactions] [greater than or equal to] .0697), military occupation ([P.sub.interactions] [greater than or equal to] .8055), or military rank ([P.sub.interactions] [greater than or equal to] .3072).

Rates of COPD: Chronic Bronchitis, Emphysema, and Chronic Airways Obstruction, Not Elsewhere Classified

Over the 13-year study period, we observed 13,195 ambulatory medical encounters for chronic bronchitis (ICD-9 491), 2,467 encounters for emphysema (ICD-9 492), and 11,020 encounters for chronic airways obstruction, not elsewhere classified (ICD-9 496). The average of the annual rates for these outcomes were very low, ranging from less than one case per 10,000 person-years (emphysema) to less than 2 cases per 10,000 person-years (chronic bronchitis and CAO) when estimated using the primary case definition (Table 3). Requiring at least 2 encounters within 2 years lowered the rates of these 3 conditions to less than 1 case per 10,000 person-years.

Rates for chronic bronchitis varied by branch of service, with Coast Guard personnel having an average rate that was significantly higher than all other service branches by between 1 and 2 cases per 10,000 person-years (P < .0001). Rates of emphysema were highest, on average, among Army personnel. Both Air Force and Marine Corps personnel had emphysema rates that were significantly lower than those in the Army (P < .0255). The average rates of CAO were highest among Army personnel and Air Force personnel, and significantly lower among Marine Corps (P < .0001), Navy (P = .0021), and Coast Guard (P < .0477) personnel, relative to Army personnel.

Personnel in combat occupations had lower rates of chronic bronchitis (P < .0051), emphysema (P = .1147), and CAO (P < .0002) relative to those in other military occupation categories. Senior personnel had higher rates of chronic bronchitis (P < .0001), emphysema (P [less than or equal to] 0788), and CAO (P < .0001), relative to junior personnel.

Overall, there was a statistically significant downward trend in the rate of chronic bronchitis ([P.sub.trend] < .0264) over the 13-year period, a small increase over time in emphysema rates that was borderline statistically significant ([P.sub.trend] = .0785), and almost no change in the rates of CAO ([P.sub.trend] = .9547) over the study period (Table 4). For each of these outcomes, the average annual change was less than one case per 10,000 person-years. Although rates were lower, the decreasing trend in rates of chronic bronchitis over time was similar when using the case definition requiring at least 3 encounters for chronic bronchitis within 2 years ([P.sub.trend] = .0241). No linear trend over time was observed using the case definition requiring at least 3 encounters for chronic bronchitis in a 2-year period ([P.sub.trend] = .434) (Figure 2). Increasing linear trends in emphysema rates over time were observed using the second case definition ([P.sub.trend] = .0555) and third case definitions ([P.sub.trend] = .0385) (Figure 3). Using the more specific case definitions of CAO resulted in a reversal in the downward trend observed for the primary case definition, although the linear trends were not statistically significant (p [greater than or equal to] .3494) (Figure 5).

[FIGURE 1 OMITTED]

Statistically significant interactions between year of diagnosis and branch of service were not observed for chronic bronchitis rates ([P.sub.interactions] [greater than or equal to] .06) but were observed by rank, with the downward trend in rates being attenuated for senior enlisted personnel ([P.sub.interactions] = .0260) and junior officers ([P.sub.interactions] = .0028), relative to junior enlisted personnel. Statistical interactions were observed between year and branch of service for emphysema and CAO rates, specifically for Navy ([P.sub.interactions] [less than or equal to] .0021) and Air Force ([P.sub.interactions] [less than or equal to] .0323) personnel.

A statistically significant interaction between year of diagnosis and military occupation was observed for CAO, with the slope of the downward trend in the rate over time attenuated among personnel in combat occupations, relative to those with noncombat military occupations ([P.sub.interactions] = .0302). A similar interaction was not observed between military rank and both CAO rates over time ([P.sub.interactions] > .2012) and rates of emphysema over time ([P.sub.interactions] > .3627).

Rates of Asthma

We observed 177,234 ambulatory medical encounters for asthma (ICD-9 493) over the 13-year period, yielding an average annual rate of 49.1 cases per 10,000 person-years (95% CI: 40.5-59.4) using the primary definition (Table 3). Requiring only one ambulatory encounter to qualify as an asthma case resulted in a considerably higher rate (91.9 cases per 10,000 person-years (95% CI: 76.9-109.9)), while requiring at least 3 encounters within 2 years decreased the rate to 32.8 cases per 10,000 person-years (95% CI: 26.2-41.0). Among the conditions assessed, asthma diagnoses were the most persistent (Table 2).

Independent of the year of diagnosis, rates of asthma varied by branch of service. Asthma rates were highest among Army personnel and at least 28 cases per 10,000 person-years lower in all other branches (P < .0001). Asthma rates were 27.1 cases per 10,000 person-years higher, on average, among those with noncombat military occupations, compared to those with combat occupations (P < .0001). Asthma rates were highest among junior enlisted personnel, and significantly lower among senior enlisted (P < .0001), junior officer (P < .0001), and senior officer (P < .0001) personnel.

Overall, there was a statistically significant linear trend over time in the rate of asthma, with the rate decreasing annually by an average of 6.3 cases per 10,000 person-years ([P.sub.trend] = .0019) (Table 4). The slope of the time trend in asthma rates varied by branch of military service ([P.sub.interactions] < .0001). Time trends in asthma rates between 2001 and 2013 did not differ significantly by military rank ([P.sub.interactions] [greater than or equal to] .4931) or category of military occupation ([P.sub.interactions] > .3150). Although the magnitude of asthma rates differed when using alternative case definitions, similar statistically significant downward trends in asthma rates over time were observed when using case definitions requiring only one asthma-coded encounter ([P.sub.trend] < .0001) and at least 3 encounters ([P.sub.trend] = .0106) with asthma (Figure 4).

Rates of Bronchiectasis and Extrinsic Allergic Alveolitis

We observed 1,196 ambulatory medical encounters for bronchiectasis (ICD-9 494) and 680 for extrinsic allergic alveolitis (ICD-9 495) over the 13-year period (Table 2). Requiring at least 2 encounters within 2 years for our primary case definition resulted in estimated incidence rates that were less than 3 cases per 100,000 person-years. Although we analyzed the trends in rates of these conditions, we present only minimal results, because the rates for these conditions were so low. There was no statistically significant evidence that time trends in the rates of either bronchiectasis or extrinsic allergic alveolitis varied over time ([P.sub.trend] >.2066), nor that trends were modified by branch of military service ([P.sub.interactions] [greater than or equal to] .3408), military occupation ([P.sub.interactions] [greater than or equal to] .0827), or military rank ([P.sub.interactions] [greater than or equal to] .1386).

COMMENT

The purpose of this study was to estimate and evaluate longitudinal trends in rates of chronic respiratory conditions in the active duty US military population from 2001 through 2013. We observed downward trends in the rates of chronic bronchitis and asthma over the study period, almost no change in the annual rates of chronic airways obstruction, and a nonstatistically significant increase in the rates of emphysema. Our findings are not consistent with a hypothesis that there have been persistent increases in the rates of respiratory illnesses in the US armed forces over the past decade. (20)

The majority of ambulatory encounters in the large group of chronic obstructive respiratory conditions were given a diagnosis of bronchitis, not specified as acute or chronic (ICD-9 490). Across the entire time period, the average rate of this nonspecific bronchitis diagnosis was more than double that for any of the other diagnoses assessed in this investigation. Rates for bronchitis, not specified as acute or chronic, increased from 2001 to 2009, and then decreased from 2009 through the end of the study period in 2013. Although we have not identified a definitive explanation for the increase in these rates between 2001 and 2009, nor for the subsequent decrease in the rates, this diagnostic category likely includes a large proportion of patients who have acute bronchitis or a similar condition. Requiring evidence of persistence of the diagnosis in the medical record by stipulating that cases have at least 2 ambulatory encounters within 2 years, for example, resulted in a dramatic drop in the estimated rate of this diagnosis, more so than for any other of the conditions we assessed. Similar f-shaped patterns were observed among all military branches and across all categories of military rank and occupation. The slope of the trends in the conditions over time frequently varied by the service branch of the US armed forces, although not in a manner that was consistent across diagnoses.

[FIGURE 2 OMITTED]

In a study with up to 4 years of post-deployment follow-up, Abraham et al observed a 25% increase in the rate of medical encounters for respiratory symptoms (RR = 1.25; 95% CI: 1.20-1.30) and a greater than 50% increase in the rate of asthma (RR = 1.54; 95% CI: 1.33-1.78) among personnel formerly deployed in support of Operation Iraqi Freedom (OIF), relative to a nondeployed reference group of personnel stationed in the United States. (13) This same study found elevated rates of medical encounters for COPD and allied conditions, although the increased rates were generally not statistically significant.

Szema et al reported an elevated risk of asthma (OR = 1.88; 95% CI: 1.38-2.56) among patients who had visited OIF/Operation Enduring Freedom (OEF) clinics at a Veterans Administration Medical Center (VAMC) in Long Island, NY, relative to patients at the same VAMC who had not visited the OIF/OEF clinics. (14) Szema et al also reported a statistically significant increase in the proportion of patients with respiratory symptoms and a greater proportion with referrals for spirometry (OR = 1.88; 95% CI: 1.38-2.56) among Veterans attending the OIF/OEF clinics, relative to a reference group of Veterans who were patients at the VAMC, but who did not visit the OIF/OEF clinics. (15) Among those referred for spirometry in this later study, both groups had similar forced expired volume in one second/forced vital capacity ([FEV.sub.1]/FVC) ratios.

Smith et al found deployment to be associated with newly reported respiratory symptoms among military personnel and Veterans participating in the Millennium Cohort Study. (19) This association was modified by branch of military service, being lowest among Navy/Coast Guard personnel (OR = 1.06; 95% CI: 0.86-1.32), and highest among Army personnel (OR = 1.73; 95% CI: 1.57-1.91). Chronic bronchitis or emphysema and asthma rates were not significantly elevated among those who had deployed relative to those who had never deployed. Although not explicitly stated by the authors, the maximum follow-up time for the Millennium Cohort analysis was approximately 4 years (OEF began in the Fall of 2001, and the study used data from questionnaires returned between June 2004 and February 2006).

Using outpatient medical encounter diagnosis data to estimate rates of chronic obstructive lung conditions allowed for efficient and large-scale assessment of trends over a long period of time. There is a time-lag between true incidence of a condition and clinical diagnosis for that condition that is not accounted for in this investigation. However, on average, it is unlikely that the magnitude of this lag changed over the study period.

False-positive and false-negative misclassification of health outcomes is also likely to have occurred. To address this limitation, we used 2 additional case definitions: a more sensitive definition that did not require evidence of persistence of the diagnosis and a more specific case definition that required cases to have at least 3 ambulatory encounters with the same ICD-9 coded diagnosis within 2 years.

Using case definitions requiring evidence of persistence of the diagnosis over time resulted in much lower estimated rates for the conditions we assessed. This is consistent with a hypothesis that many ambulatory encounters are assigned specific diagnostic codes corresponding to chronic obstructive respiratory conditions but do not meet diagnostic criteria for those condtions. (21) These transient findings may reflect working diagnoses which change over time, imprecise coding, or misdiagnoses. Although the rates were lower, the overall temporal pattern observed in the rates of unspecified bronchitis, chronic bronchitis, and asthma were similar when using less sensitive, but more specific, case definitions. However, we did note qualitative differences in temporal trends for emphysema and CAO. The rising temporal trend in emphysema became borderline statistically significant when requiring at least 2 encounters within a 2 year period, and was statistically significant when requiring at least 3 encounters within 2 years. The downward temporal trend observed using our primary case definition of CAO reversed direction when using the more specific case definitions, although the rising temporal trends we observed were not statistically significant.

Regardless of the specificity of the case definition, false-positive cases would have resulted from ambulatory care encounters that are assigned an incorrect or inappropriate ICD-9 code. Additionally, an unknown number of incident chronic obstructive lung conditions likely remain undiagnosed and therefore not enumerated in our study (false-negatives). If the degree of misclassification remained constant over the study period, the estimated rates would be biased, but the trends in rates would remain unbiased. Changes in the frequency of outcome misclassification over time, due to changes in coding practices, for example, would result in biased time trends as well.

Potential explanations for the observed relationships between time and health condition rates include confounding by time-varying predictors of obstructive pulmonary condition diagnoses, such as an external factor that changes from year to year, similar to rates of flu. Subsequent work will attempt to parse out these possible co-relationships so that trends independent of these confounders can be evaluated.

Rates of chronic obstructive conditions during this time period were generally low, and similar to, or lower than, corresponding rates in the general population. (2)

Branch of military service, military rank, and job category were associated with rates of chronic obstructive pulmonary conditions defined using ambulatory medical encounter data. A decreasing temporal trend in asthma rates was consistently observed. Trends in bronchitis rates, too, generally decreased over time, with the notable exception of the those for bronchitis, not specified as acute or chronic, which increased significantly between 2001 and 2009. This assessment did not discriminate between military personnel with and without a history of deployment to Southwest Asia. Future work should focus on assessing rates of these conditions among personnel with prior history of deployment in support of OEF, OIF, and Operation New Dawn.

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REFERENCES

(1.) Akinbami LJ, Moorman JE, Liu X. Asthma prevalence, health care use, and mortality: United States, 2005-2009. Natl Health Stat Report. 2011;(32):1-14.

(2.) Chronic obstructive pulmonary disease among adults-United States, 2011. MMWR Morb Mortal Wkly Rep. 2012;61(46):938-943.

(3.) Kochanek KD, Xu J, Murphy SL, Minino AM, Kung H. Deaths: final data for 2009. Natl Vital Stat Rep. 2011;60.

(4.) Absolute and relative morbidity burdens attributable to various illnesses and injuries, US Armed Forces, 2011. MSMR. 2012;19:4-8; discussion 8-9.

(5.) Carlson KF, Nelson D, Orazem RJ, Nugent S, Cifu DX, Sayer NA. Psychiatric diagnoses among Iraq and Afghanistan war veterans screened for deployment-related traumatic brain injury. J Trauma Stress. 2010;23(1):17-24.

(6.) Kelly JF, Ritenour AE, McLaughlin DF, et al. Injury severity and causes of death from Operation Iraqi Freedom and Operation Enduring Freedom: 2003-2004 versus 2006. J Trauma. 2008;64(suppl 2):S21-S26; discussion S26-S27.

(7.) Milliken CS, Auchterlonie JL, Hoge CW. Longitudinal assessment of mental health problems among active and reserve component Soldiers returning from the Iraq war. JAMA. 2007;298:2141-2148.

(8.) Seal KH, Bertenthal D, Miner CR, Sen S, Marmar C. Bringing the war back home: mental health disorders among 103,788 US veterans returning from Iraq and Afghanistan seen at Department of Veterans Affairs facilities. Arch Intern Med. 2007;167:476-482.

(9.) Vasterling JJ, Proctor SP, Amoroso P, Kane R, Heeren T, White RF. Neuropsychological outcomes of Army personnel following deployment to the Iraq war. JAMA. 2006;296:519-529.

(10.) Warden D. Military TBI during the Iraq and Afghanistan wars. J Head Trauma Rehabil. 2006;21:398-402.

(11.) Shen YC, Arkes J, Williams TV. Effects of Iraq/Afghanistan deployments on major depression and substance use disorder: analysis of active duty personnel in the US military. Am J Public Health. 2012;102(suppl 1):S80-S87.

(12.) Weese CB, Abraham JH. Potential health implications associated with particulate matter exposure in deployed settings in southwest Asia. Inhal Toxicology. 2009;21:291-296.

(13.) Abraham JH, Eick-Cost A, Clark LL, et al. A retrospective cohort study of military deployment and post-deployment medical encounters for respiratory conditions. Mil Med. 2014;179(5):540-546.

(14.) Szema AM, Peters MC, Weissinger KM, Gagliano CA, Chen JJ. New-onset asthma among Soldiers serving in Iraq and Afghanistan. Allergy Asthma Proc. 2010;31(5):67-71.

(15.) Szema AM, Salihi W, Savary K, Chen JJ. Respiratory symptoms necessitating spirometry among Soldiers with Iraq/Afghanistan war lung injury. J Occup EnvironlMed. 2011;53:961-965.

(16.) Baird CP, Debakey S, Reid L, Hauschild VD, Petruccelli B, Abraham JH. Respiratory health status of US Army personnel potentially exposed to smoke from 2003 Al-Mishraq sulfur plant fire. J Occup Environl Med. 2012;54:717-723.

(17.) Abraham JH, DeBakey SF, Reid L, Zhou J, Baird CP. Does deployment to Iraq and Afghanistan affect respiratory health of US military personnel?. J Occup Environl Med. 2012;54:740-745.

(18.) Abraham JH, Baird CP. A case-crossover study of ambient particulate matter and cardiovascular and respiratory medical encounters among US military personnel deployed to southwest Asia. J Occup Environl Med. 2012;54:733-739.

(19.) Smith B, Wong CA, Smith TC, Boyko EJ, Gackstetter GD. Newly reported respiratory symptoms and conditions among military personnel deployed to Iraq and Afghanistan: a prospective population-based study. Am J Epidemiol. 2009;170:1433-1442.

(20.) Kennedy K. Health alert: respiratory problems, neurological conditions and heart disease on rise since 2001. Air Force Times. October 14, 2010;news:10-11.

(21.) Tokunbo M, Abraham JH, Zacher LL, Morris MJ. The impact of deployment on COPD in active duty military personnel. Mil Med. 2014. In press.

* Tricare is the Department of Defense health care program for members of the uniformed services, their families, and their survivors. Information available at http://www.tricare.mil.

Joseph H. Abraham. ScD

Leslie L. Clark, PhD

Jessica M. Sharkey, MPH

Coleen P. Baird, MD, MPH

Dr Abraham is an Epidemiologist, Environmental Medicine, US Army Public Health Command, Aberdeen Proving Ground, Maryland.

Dr Clark is a Senior Managing Epidemiologist in the Epidemiology and Analysis Division, Armed Forces Health Surveillance Center, Silver Spring, Maryland.

Ms Sharkey is an Epidemiologist, Environmental Medicine, US Army Public Health Command, Aberdeen Proving Ground, Maryland.

Dr Baird is Program Manager, Environmental Medicine, US Army Public Health Command, Aberdeen Proving Ground, Maryland.
Table 1. Demographic and military characteristics,
active component service members, 2001-2013. *

                                n        %

Gender
  Male                      3,189,666   83.9
  Female                      611,010   16.1
Service
  Army                      1,454,958   38.3
  Navy                        890,350   23.4
  Air Force                   784,278   20.6
  Marine Corps                587,395   15.5
  Coast Guard                  83,695    2.2
Rank
  Junior Enlisted (E1-E3)   2,506,273   65.9
  Senior Enlisted (E4-E6)     873,722   23.0
  Junior Officer (O1-O3)      329,815    8.7
  Senior Officer (O4-O6)       90,866    2.4
Military occupation
  Combat                      818,644   21.5
  Healthcare                  277,607    7.3
  Other                     2,704,425   71.2
Age group (years)
  <20                         475,754   12.5
  20-24                     1,801,244   47.4
  25-29                       793,778   20.9
  30-34                       451,184   11.9
  35-39                       191,551    5.0
  40-44                        64,255    1.7
  45-49                        17,327    0.5
  50-54                         3,971    0.1
  [greater than or                168    0.0
    equal to] 55
Race, ethnicity
  White, nonhispanic        2,419,033   63.6
  Black, nonhispanic          610,109   16.1
  Other/unknown               771,534   20.3

* This is a dynamic population. To characterize
time-varying characteristics (age and occupation),
we identified all individuals in service for
at least one day during the surveillance period
(the population at risk), then identified the
demographic record closest to the midpoint of
their period of service and used that record to
identify age and military occupation.

Data Source: Defense Medical Surveillance
System.

Table 2. Number and percentage of cases of selected chronic
respiratory conditions in the US military from 2001-2013,
by ICD-9-coded condition.

Respiratory             ICD-9    Primary Case
Condition                Code    Definition *

                                   n         %

Bronchitis,              490     55,853    35.5
  not specified as
  acute or chronic
Chronic bronchitis       491      2,085     1.3
Emphysema                492        826     0.5
Asthma                   493     94,858    60.2
Bronchiectasis           494        488     0.3
Extrinsic allergic       495        104     0.1
  alveolitis
Chronic airways          496      3,302     2.1
  obstruction, not
  elsewhere
  classified

Respiratory             Sensitive Case    Specific Case
Condition               Definition *      Definition *

                           n         %      n         %

Bronchitis,             276,878    57.4   14,575    17.8
  not specified as
  acute or chronic
Chronic bronchitis       13,195     2.7      761     0.9
Emphysema                 2,467     0.5      427     0.5
Asthma                  177,234    36.7   64,026    78.2
Bronchiectasis            1,196     0.2      316     0.4
Extrinsic allergic          680     0.1       55     0.1
  alveolitis
Chronic airways          11,020     2.3    1,683     2.1
  obstruction, not
  elsewhere
  classified

* The primary case definition required at least 2 ambulatory
medical encounters recorded in DMSS with identical ICD-9 codes
within 2 years (730 days). The more sensitive case definition
required only a single ambulatory medical encounter with a given
ICD-9 code. The more specific case definition required at least
3 ambulatory medical encounters recorded in the DMSS with
identical ICD-9 codes within 2 years.

Data Source: Defense Medical Surveillance System.

Table 3. Average rates with 95% confidence intervals of chronic
respiratory conditions in the U.S. military for the 2001-2013 study
period. *

Chronic Respiratory               Average Rate        95%
Condition ([dagger])               per 10,000     Confidence
                                  Person-years     Interval

                                                 Lower   Upper
                                                 Limit   Limit

Bronchitis,
  not specified as acute or
  chronic (ICD-9 490)
    Primary case definition          27.73        21.43-35.88
    Sensitive case definition        144.30      122.89-169.45
    Specific case definition          7.00          5.1-9.5
Chronic bronchitis (ICD-9 491)
    Primary case definition           1.10         0.95-1.26
    Sensitive case definition         6.45         4.82-8.63
    Specific case definition          0.40         0.34-0.47
Emphysema (ICD-9 492)
    Primary case definition           0.43         0.37-0.50
    Sensitive case definition         1.31         1.20-1.44
    Specific case definition          0.21         0.17-0.27
Asthma (ICD-9 493)
    Primary case definition          49.05        40.49-59.42
    Sensitive case definition        91.89       76.86-109.86
    Specific case definition         32.78        26.18-41.03
Bronchiectasis (ICD-9 494)
    Primary case definition           0.24         0.18-0.32
    Sensitive case definition         0.63         0.56-0.71
    Specific case definition          0.15         0.10-0.21
Extrinsic allergic alveolitis
  (ICD-9 495)
    Primary case definition           0.05         0.05-0.06
    Sensitive case definition         0.31         0.22-0.45
    Specific case definition          0.03         0.02-0.04
Chronic airways obstruction,
  not elsewhere classified
  (ICD-9 496)
    Primary case definition           1.73         1.47-2.02
    Sensitive case definition         5.81         5.10-6.62
    Specific case definition          0.86         0.70-1.06

* Averages were calculated by exponentiating the average of natural
log-transformed annual encounter rates.

([dagger]) The primary case definition required at least 2 ambulatory
medical encounters recorded in DMSS with identical ICD-9 codes within
2 years (730 days). The more sensitive case definition required only
a single ambulatory medical encounter with a given ICD-9 code. The
more specific case definition required at least 3 ambulatory medical
encounters recorded in the DMSS with identical ICD-9 codes within 2
years.

Data Source: Defense Medical Surveillance System.

Table 4. Trends in rates of encounters with chronic obstructive
pulmonary diseases and allied conditions (ICD-9 490-496) in the
US military, 2001-2013, by diagnosis. *

Chronic Obstructive   ICD-9   Percentage   95% Confidence  P value
Pulmonary Disease     Code     Increase       Interval
or Allied Condition            in Trend
                              ([dagger])

                                           Lower   Upper
                                           Limit   Limit

Bronchitis,            490      -2.54%     -3.56   -1.51   0.0003
  not specified as
  acute or chronic
  ([double dagger])
Chronic bronchitis     491      -3.61%     -6.60   -0.52   0.0264
Emphysema              492      3.47%      -0.46   7.55    0.0785
Asthma                 493      -5.91%     -9.23   -2.47   0.0033
Bronchiectasis         494      4.69%      -2.89   12.85   0.2066
Extrinsic allergic     495      2.35%      -2.40   7.33    0.3057
  alveolitis
Chronic airways        496      0.12%      -4.24   4.67    0.9547
  obstruction,
  not elsewhere
  classified

* Rates were estimated using a case definition that required
evidence of persistence of the diagnosis in the medical record,
i.e., at least 2 encounters with the same diagnosis code within
2 years.

([dagger]) The percent increase in the linear slope is derived
from the slope estimate from a regression model of year as a
continuous independent predictor of natural log-transformed
rates.

([double dagger]) A statistically significant curvinear trend
was observed for the bronchitis, not specified as acute or
chronic outcome. As such, we present only the percent change in
the quadratic, derived from the quadratic term from a regression
model of [year.sup.2] as a continuous independent predictor of
natural log-transformed rates in a model that also contains the
main effect of year as a continuous independent predictor.

Data Source: Defense Medical Surveillance System.
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Article Details
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Author:Abraham, Joseph H.; Clark, Leslie L.; Sharkey, Jessica M.; Baird, Coleen P.
Publication:U.S. Army Medical Department Journal
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2014
Words:6037
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