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An outbreak of pertussis-like syndrome in Boulder County, Colorado.

An Outbreak of Pertussis-like Syndrome in Boulder County, Colorado

The yearly incidence of pertussis in the U.S. declined dramatically with the introduction of pertussis vaccine.[1] Unfortunately, sporadic cases and occasional outbreaks still occur,[2-5] and cases reported to the Centers for Disease Control increased from 1982-1986 with only 1987 showing a decrease in reports.[6] Efforts to maintain high immunization rates among preschool and school-age children have been hampered by unfavorable publicity surrounding pertussis vaccine.[7] Health care providers, in particular school nurses, should anticipate additional cases and outbreaks if the current trend continues.


The Boulder County (Colo.) Health Department investigated an outbreak of pertussis-like syndrome that occurred from July through December 1988. The outbreak centered at a private elementary school (enrollment 185) with some spread to a public elementary school (enrollment 425). Both schools are experiential-based learning centers with diverse student populations, where a significant proportion of parents choose alternative approaches to health care for themselves and their children.

The public school district contracts with the county health department for school health services. School nurses hired under this contract work exclusively in the public schools, whereas most school nurses in Colorado are not associated with a health department. Historically, school nurses have provided measures to control the spread of communicable diseases among school-age children.[8] The private school involved in the outbreak does not maintain a school nurse of other health care service.

A case of pertussis was defined as an illness that was either: a) confirmed by positive culture and/or direct fluorescent antibody testing (FA) for Bordetella pertussis, b) diagnosed as pertussis by a physician, or c) characterized by a cough lasting 14 consecutive days or more that had either inspiratory whoop, post-tussive vomiting, or a household member with laboratory confirmed or clinically diagnosed pertussis.

Initial cases were detected through direct physician reports to the local health department. Active surveillance for additional cases included weekly telephone contact with area physicians and school-based surveillance at the two schools for any recent coughing illnesses. The school nurse performed case finding at the public school. The private school relied on teachers to survey students for suspect illnesses. All reported cases were subsequently investigated by the health department and all relevant demographic, clinical, epidemiologic, laboratory, and immunization information was obtained.

A DTP immunization audit was conducted at the private school by the Colorado Department of Health immunization program and at the public school by the assigned school nurse. Children were considered appropriately immunized if their records indicated a minimum of four doses of DTP by age five. Though five doses of DTP vaccine are recommended by the US Public Health Service Immunization Practices Advisory Committee[8] and the American Academy of Pediatrics,[9] four doses meets the minimum state requirement set by the Colorado Department of Health for school-age children.[10]

Both schools used the same approach to control transmission of pertussis. Control efforts consisted of sending a letter home informing parents of the outbreak and the signs and symptoms of pertussis. The letter recommended that contacts be treated with antibiotics for 14 days, and required children suspected of having pertussis be kept home from school or out of day care for five days after beginning antibiotic therapy, or for 21 days after onset of symptoms if no antibiotic was taken. In addition, the county health department encouraged parents to consider the DTP vaccine for all children under age seven who were not age-appropriately immunized. The school nurse augmented these control measures in the public school by having direct contact with the teachers, students, and parents to answer questions and provide information.


Investigation revealed 34 individuals meeting the case definition for pertussis-like syndrome. Of these, 21 occurred at the private elementary school. One additional case occurred at the public elementary school with the remainder of cases being family contacts. No one was hospitalized. However, two children reported experiencing 20-second seizures and two other children developed mild cases of pneumonia as a complication of their primary illness. None of the 14 children tested for B pertussis was positive by culture or direct fluorescent antibody testing.

The earliest reported illnesses appeared during the first week in July 1988 (Figure 1). The epidemic curve shows a few sequential cases during the summer with an increasing incidence occurring in the autumn school semester. Active surveillance revealed no further onset of pertussis-like illness past the second week of December. The mean age at onset of symptoms was eight years with a concentration of cases between the ages of five and nine corresponding to elementary grades K-4. Distribution of ages ranged from four months to 46 years.

The overall attack rate for students who attended the private school was 11.4% (21/185) and 0.002% (1/425) at the public school. At the private school, the attack rate for children who had less than the state recommended level of four DTP immunizations was 24.4% compared to 3.8% for those who had received four or more immunizations (odds ratio 8.4, 95% CI 2.03,34.79).[11] Since private school students showed varying levels of DTP immunizations, a linear regression test (chi-square) was performed, indicating a highly significant trend of decreasing incidence with increasing immunization levels (p [is less than] .000).[12]


Though none of the 14 cases tested was fluorescent antibody or culture positive, evidence suggests that B pertussis was the likely etiologic agent. Unfortunately, most laboratory specimens were obtained several weeks after onset of symptoms when results would most often be negative. When comparing unimmunized private school students with those who had three or more DTP shots, unimmunized students were eight times more likely to develop symptoms of pertussis.

The clinical picture among identified cases was consistent and in most cases presented with classic whooping cough symptoms. The youngest patient, a four-month-old male, had 20-second generalized seizures after some of his paroxysms. Several parents reported they feared for their children's lives during the worst of the illness. Investigation suggests the outbreak began early in July 1988 among students who would be attending the private elementary school in the fall, and eventually spread to the public elementary school as well as additional family members.

The two elementary schools involved in the outbreak follow similar teaching philosophies. While the private school exists independently, the public school is unique among the 28 elementary schools in the district. Like the private school, the public school provides an experiential-based curriculum and open enrollment. Each school strives for a diverse cultural and socioeconomic mix of students and frequent crossover of students occurs between schools.

A high proportion of the student's families see alternative health care providers and are averse to immunizations for their children. Compliance with state immunization laws was and still is difficult at both schools. Personal exemptions for religious or personal reasons were signed for 7% of the public school population, and nearly one-quarter (23%) of private school students were exempted from immunizations.

The health department was notified of suspected pertussis well after the disease had occurred at the private elementary school. Had a school nurse been available, the emerging disease pattern probably would have been brought to the attention of school authorities and the local health department much sooner. The private elementary school does not retain the services of a school nurse. Instead, they rely on teachers, assistants, and administrators to exercise good judgment in assessing illnesses or accidents. This incident demonstrated the acute need of a school nurse's presence before an outbreak occurs.

Attempts were made to initiate ongoing surveillance for newly arising cases at both schools. The health department directed the private school to have teachers survey students for coughing illnesses and report to the administrator's secretary. In the public school, the nurse personally spoke with students in each exposed classroom to detect suspect coughing illnesses, which led to open discussions among students and teachers regarding the clinical signs and symptoms of pertussis. The public school maintained a higher awareness of the situation, and the school nurse provided detailed descriptions of suspect illnesses. Several pertussis cases at the private school were not detected through the school-based surveillance system, but were brought to the attention of the investigators by reports from concerned parents.

Letters were sent home with the children identified as having potential exposure to B pertussis, apprising parents of the situation and providing recommendations for appropriate antibiotic prophylaxis. Compliance was difficult at each school. At the public school, follow-up information was provided by the school nurse to parents who expressed apprehension about administering 14 days of antibiotic therapy to an asymptomatic child. Distrust of the traditional health care system prompted several parents to consult the nurse about the necessity of the recommendations. The availability of a nurse to answer questions concerning the outbreak reassured parents. Their acceptance of the nurse's advice was predicated on confidence and trust developed from previous interactions and experiences.

Another important aspect of having a school nurse participate in the control of the outbreak was the immediate access to the school available to the local health department. Conversely, the school district had access to resources from the health department. Without access through a school nurse, health departments must arrange with school administrators for access before investigations can begin.


The school nurse was important in the outcome of this infectious disease outbreak in a school setting. This observation seems especially important considering school administrators often seek to balance budgets by eliminating or reducing health services. This incident illustrated that inadequately trained school staff cannot substitute for the professionalism of a school nurse. Differences in immunization promotion, early disease detection, case finding, accessibility, and compliance with control efforts between the public and private elementary schools were significant and affected the magnitude and duration of the outbreak.


[1]Cherry JD, Brunell PA, et al. Report of the Task Force on pertussis and pertussis immunization - 1988. Pediatrics. 1988;81(6): part 2. [2]Nkowane BM, Steven GF, et al. Pertussis epidemic in Oklahoma, difficulties in preventing transmission. Am J Dis Child. 1986;140:433-437. [3]Centers for Disease Control. Pertussis - United States, 1982-83. MMWR. 1984;33:573-575. [4]Centers for Disease Control. Pertussis - Maryland. MMWR. 1983;32:297-305. [5]Pugh EJ. Whooping cough in Wear Valley 1983 and 1984. Public Health. 1986;100:11-14. [6]Centers for Disease Control. Summary of notifiable diseases, United States, 1987. MMWR. 1988;36(54):suppl. [7]Gonzales ER. TV report galvanizes US Pediatricians. JAMA. 1982;282:12-22. [8]Immunization Practices Committee. Diphtheria, tetanus, and pertussis: Guidelines for vaccine prophylaxis and other preventive measures. MMWR. 1985;34:405-414, 419-426. [9]American Academy of Pediatrics. Report of the committee on infectious diseases. 21st ed. Evanston, Ill: American Academy of Pediatrics; 1988. [10]Colorado Board of Health. Revised rules of the Colorado Board of Health pertaining to the immunization of children attending school. 1983. [11]Thomas DG. Exact and asymptotic methods for the combination of 2 x 2 tables. Comput Biomed Res. 1985;8:423-466. [12]Rothman KJ, Boice JD. Epidemiologic analysis with a programmable calculator. Bethesda, Md: NIH pub no 79-1649; June 1979.
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Author:Lenaway, Dennis D.; Ambler, Audrey; Brockmann, Robert A.; Bailey-Britton, Ann; Cruz-Uribe, Federico
Publication:Journal of School Health
Date:Jan 1, 1990
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