Tuberculosis related to labor activity in an area of Valencia, Spain.

Introduction

The incidence of tuberculosis (TB) is increasing in nearly every region of the world (1). A number of factors have led to increased incidence in economically developed countries; these factors include the human immunodeficiency virus (HIV) epidemic, homelessness, and immigration from areas in which TB is highly endemic (2).

TB case notifications are also clearly increasing in economically developing countries. Increases are to be found in four World Health Organization (WHO) regions: Africa, the eastern Mediterranean, southeast Asia, and the western Pacific. By contrast, the average number of cases has decreased in the American and European regions. With the exception of Portugal, all western European countries have reported TB rates of less than 25 per 100,000 per year (3).

In this context, Spain is one of the most affected countries in Europe, with a clearly ascending trend (4). According to official 1991 statistics, the prevalence of TB in Europe as a whole is 27 per 100,000 inhabitants, while the prevalence in Spain is 36 per 100,000. Indirect estimates suggest that in 1994 the incidence of TB in Spain was around 60 per 100,000 per year (4).

The risk of occupational exposure to TB has increased among

* health care and other workers exposed to persons with active TB,

* workers exposed to silica or other agents that increase the risk of progression from latent infection to active TB, and

* workers in occupations associated with low socioeconomic status. [TABULAR DATA FOR TABLE 1 OMITTED] In subjects who have previously suffered from focal pulmonary TB, recurrences most often arise secondary to associated conditions such as HIV, chronic bronchitis, chronic alcoholism, and occupational hazards (5).

The present study compares the characteristics of TB in different professional groups in relation to the demographic and occupational parameters of the surrounding population in Valencia. The goal is to tie the results to public health actions.

Materials and Methods

Over a period of five years, the authors made a descriptive study of 374 case histories of adult patients diagnosed with TB at the Service of Internal Medicine of the La Fe University Hospital in Valencia, Spain.

The Valencian community comprises three provinces on the Spanish Mediterranean coast: Valencia, Castellon, and Alicante. The area served by the La Fe University Hospital is the largest health care coverage area in the Valencian community, consisting mainly of two zones in Valencia Province: an urban area (Valencia City) and a rural region (towns surrounding the city). During 1985, a total of 57,818 adult patients were admitted to this hospital, which had an occupation rate of 80.6 percent. The mean hospital stay was 9.88 days for all causes.

The following data were gathered from the TB case histories: sex, age, civil status, and origin (rural or urban). The Spanish National Institute of Statistics defines a rural environment as an environment that has a population of under 10,000 and that is not influenced by a nearby urban area. Likewise, an urban area is defined as having a population of over 10,000. Additional data collected from the case histories included profession and hospitalization (based on the classification used by Perez-Tomas) (6). Information also was gathered about toxic habits (tobacco, alcohol ingestion, and intravenous drug addiction); pathology (note was taken of associated disease and earlier pathology with possible repercussions on TB); mortality; and disease characteristics. In this context, the different TB presentations were classified as

* lung TB,

* lung infiltration TB,

* lung infiltration TB with cavity,

* nonspecific lung TB,

* TB pleurisy, or

* other forms of TB.

Using the classification system developed by Rodriguez-Ramos, the authors evaluated whether TB was suspected upon hospital admission; also, the location of the disease was noted, along with symptomatology upon admission and TB-associated complications (7,8).

According to the Spanish National Classification of Occupations, the professional groups considered in this study were liberal professionals and technicians; public administration directors and company managers; administrative personnel; store owners and sales personnel; services and security personnel; agricultural, farm, and fishing industry workers; miners and mineral-processing workers; machinery, construction, and transport workers, domestic labor; students, pensioners, and retired individuals; individuals without classification; and the unemployed (9). Individuals without classification included the following groups: patients infected with HIV and patients suffering from the acquired immunodeficiency syndrome (AIDS). In the present study, mention is made of HIV-positive individuals and patients with AIDS only when these conditions are associated with TB.

The employment structure in Valencia province centers around agriculture, industry, services, and an inactive population, according to the National Institute of Statistics. The agricultural sector comprises agriculture, farm workers, and the fishing industry. The industry sector involves liberal professions, technicians, public administration directors and company managers, administrative personnel, and miners and mineral workers. The services sector comprises store owners, sales personnel, services, domestic workers, and security personnel. Finally, the inactive sector involves domestic labor, pensioners, students, and the unemployed (9).

The working protocol consisted of 191 variables that were coded and processed with the SPSS PC+ software package. The population served by the La Fe University Hospital and the global population of the Valencian community were grouped together for comparison with the study group. The aim was to establish comparisons by means of the Z-proportions contrast test (p [less than] .01) (10).

The odds ratio (OR) was calculated to establish differences in risk between the study population (374 cases of TB) and the hospital coverage population (controls), both of which were selected according to the information provided by the same hospital. The coverage population included both groups, and both were classified by professional sectors: agriculture, industry, construction, services and inactive.

The control population was used only to study the risk of developing TB for each professional sector. The industrial sector was used as estimator reference, as it involved the fewest cases of TB. The Mantel-Haenzel test was performed to control for confounding factors. The corresponding 95 percent confidence intervals (CI 95 percent) were calculated.

Results

A total of 374 cases of TB reported in the La Fe University Hospital were studied. The study population had significantly more males (n = 273, or 73 percent) than females (n = 101, or 27 percent) (p [less than] .01). Subject stratification by age interval showed significant differences (p [less than] .01) between groups. Table 1 shows associations between profession and sex, and profession and age.

Agriculture, industry, and services, accounted respectively for 10.8 percent, 42.0 percent, and 46.2 percent of the labor force in [TABULAR DATA FOR TABLE 2 OMITTED] the Valencian community (11). In the study populations, the most common occupations were mining, construction, and transport activities (28.2 percent), followed by farming and fishing (15.8 percent).

Table 2 shows the association between the professional designations of the 374 TB patients and their toxic habits (tobacco, alcohol and intravenous drugs). In response to questions about health risk factors, 68.6 percent of the patients reported that they smoked. By comparison, approximately 54.7 percent (between 51.0 and 58.3 percent) of the general Spanish population smokes, according to the national population survey (12). In the Valencian community, approximately 62.8 percent (between 59.3 and 66.4 percent) of the population smokes, according to the Valencia community population survey (13). With respect to alcohol consumption, 40.5 percent of the study group were regular drinkers; the national and local surveys found that 71.5 percent and 55.2 percent, respectively, were regular drinkers (12,13).

The study also considered diseases and disorders associated with TB and previous diagnoses of TB in the study population (Table 3). It was found that prior pathologies (chronic obstructive lung diseases and liver disorders) had been diagnosed in 90 patients mainly working in mining and construction (86.5 percent). The numbers of patients who had associated pathologies (i.e., dyspnea, residual pachypleuritis, bronchiectasis, pulmonary insufficiency) varied significantly among the professional groups (p [less than] .01).

Seventy-five percent of the study group individuals without professional classification presented associated pathologies (fundamentally infectious in nature). In 37.8 percent of the cases, TB location was extrapulmonary. Bacteriological and histopathological studies were of fundamental importance in diagnosing patients with extrapulmonary TB. Seventeen percent of the patients with extrapulmonary TB died during hospitalization, mainly as a result of AIDS and accompanying infectious processes.

The association between profession and diagnosis of the disease is reflected in Table 4 and Table 5. The Mantoux test was positive in 67.2 percent of cases, Ziehl sputum staining in 42.0 percent of cases, and sputum culture in 51.8 percent.

Nonspecific lung TB was diagnosed in 232 patients (62.0 percent). Extrapulmonary TB was diagnosed in 21.9 percent of patients involved in domestic labor (including seven female patients) and in 19.7 percent of patients without professional classification (including seven HIV-infected subjects).

Within the entire population of patients served by the hospital, 1.0 percent worked in agriculture, 14.2 percent in industry, and 19.4 percent in the services sector; 37.2 percent were inactive. By contrast, 15.8 percent of the TB patients worked in agriculture (p = .000), 37.8 percent worked in industry (p = .000), 15.5 percent worked in the services sector (p = . 051), and 30.4 percent were inactive (p = .001).

[TABULAR DATA FOR TABLE 3 OMITTED]

The patients in our series were classified by professional sectors in the same way as the control population served by the La Fe University Hospital so that the risks incurred by different groups (agriculture, services, industry, construction and the inactive population) could be compared (Table 6). With the industrial sector as base reference, the risk of developing TB was significantly greater among patients in the agricultural sector (OR was 16.94; CI 95 percent was 11.01-26.11) and in construction work (OR was 9.64; CI 95 percent was 6.53-14.29).

[TABULAR DATA FOR TABLE 4 OMITTED]

Discussion

This study analyzed the occupational and demographic characteristics of 374 tuberculosis patients treated at the La Fe University Hospital from 1985 to 1989. The cases and their characteristics were compared with the demographic and occupational parameters of the coverage population.

TB has been characterized as one of the most socially representative diseases. In this context, it is often remarked that public health education contributes to the success of TB control programs. The disease is traditionally associated with poor living conditions, low socioeconomic status, and areas in which M. tuberculosis is endemic (14). There has been increasing interest in the potential association between occupation and the risk of TB; certain labor activities have been associated with increased TB risk.

In our study, only 27 percent of the patients were female. The much-discussed social and labor changes among women have not been observed in the Valencian community. Although a small proportion of women work in all the professional areas considered, most of the female patients in this study continue to work in the home. It should be pointed out that. along with AIDS patients, this group exhibits the highest percentage of extrapulmonary TB (19.7 percent and 21.9 percent, respectively). The higher proportion of this type of TB among women and young adults reflects the higher rate of HIV infection in these groups (15).

The situation among students is worrisome; it appears to reflect the continued high percentage of infections occurring in our environment. Many studies confirm this observation (16).

Over half (56.7 percent) of the study patients lived in a rural setting, while only 43.4 percent resided in the urban area of Valencia [TABULAR DATA FOR TABLE 5 OMITTED] City. These proportions reflect the patient base of the La Fe University Hospital, which serves a predominantly rural zone (60 percent of the population served by the hospital lives in rural areas). Also of importance is the fact that immigrant farm workers are at a greater risk of developing chronic and communicable disease (17). Other studies have confirmed the significantly increased risk to farm and industrial workers (18).

This study found the incidence of the disease to be highest among workers in agriculture, mining, and construction. A considerable number of cases, however, occurred in so-called passive individuals: housewives, students, and pensioners. Therefore, more powerful preventive and therapeutic tools need to be developed and adopted in the Valencia community.

Workers in the agricultural sector tend to be elderly individuals living in rural areas where greater control of the disease is required. Efforts are currently underway to control TB in these zones (19).

Older patients tended to work in agriculture and industry; married individuals likewise predominated in these sectors. Marital status should be taken into account when the potential for contagion is being evaluated, because married individuals are more prone to infect relatives with whom they live daily.

The consumption of tobacco and alcohol was significant in several professional sectors. In other studies, cigarette smoking and alcohol consumption have been significantly associated with the risk of TB (18). These habits are regarded as predisposing to a number of diseases, including chronic obstructive lung disease and liver pathology, which are in turn frequently associated with TB. Both parameters were observed to have statistically significant associations with TB incidence (p [less than] .001).

This study found that the number of patients with TB has stabilized in recent years. A progressive increase was noted, however, among HIV-positive individuals and among patients with AIDS - especially among intravenous drug abusers (20). Extrapulmonary locations seem to be on the rise, along with noncavitary presentations. The increase in TB incidence among younger patients may be partly due to their predominance in the HIV-positive and AIDS groups (21). Atypical localization of pulmonary TB also is frequent in HIV patients (22, 23).

The authors are aware that the risk of contracting TB has increased among health care workers - particularly among emergency ward personnel, since emergency wards often treat TB patients before diagnosis of the disease (24). A limitation of this study is the absence of health care workers in the study group; no patients belonging to this category were diagnosed with TB in the La Fe University Hospital during the study period.

Nevertheless, the labor environment can be expected to influence the incidence of TB simply because the majority of individuals spend most of their lives in the workplace. Most working days last eight hours, and most work weeks last five days, for a total of 40 hours. Work hours tend to increase when the individual runs his or her own business - as is typical in the agricultural sector. Conditioning factors in turn include social, economic, and environmental factors, as well as the way personal habits interact with the labor setting. Such factors may be expected to define those individuals most susceptible to TB (25).

TABLE 6

Risk by Professional Sector

Professional         Odds           95% Confidence      Probability
Sector               Ratio            Interval

Agriculture          16.64           11.05-25.05          .0000
Construction          9.55            6.57-13.88          .0000
Service               0.89            0.59-1.34           .5725
Inactive              0.87             0.6-1.26           .4679

The main obstacle to more rapid progress in combatting the disease remains financial. Resources available for global TB control are limited.

In view of the results obtained from this study, the authors feel that additional emphasis should be placed on the adoption of collective health care measures among people working in agriculture, as well as on establishing underlying causes and mechanisms of disease development (26). The data from this study suggest that certain occupations may be associated with an elevated risk.

The results of the study also raise a number of important issues. The finding that no cases occurred among health care workers is potentially important; it points to limited occupational risk for TB in this sector. In addition, the fact that 44 percent of all cases involved individuals associated with the mining and agricultural sectors suggests that efforts should be concentrated in these areas. It may be administratively efficient to screen at such work sites for asymptomatic infections and to provide preventive therapy in these settings - even if the acquisition of TB infection has not been shown to be causally linked to the work setting.

Corresponding Author: M. M. Morales Suarez-Varela, Unidad de Salud Publica, Higiene y Sanidad Medioambiental Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andres Estelles s/n, 46100-Burjassot, Valencia, Spain.

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