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Pertussis Outbreaks -- Massachusetts and Maryland, 1992

During November 1992, cases of pertussis among students in Massachusetts and Maryland were reported to the respective state health departments. This report summarizes the investigation of and approaches to controlling these outbreaks. Massachusetts

On November 16, 1992, a 14-year-old high school student with pertussis was reported to the Massachusetts Department of Public Health (MDPH). Onset of cough was October 14, and a serologic test performed by the Massachusetts State Laboratory Institute (MSLI) indicated that the student had an elevated level of immunoglobulin G (IgG) antibody to pertussis toxin (PT). Other students in the same high school (student population: 623 in grades 9-12) and a nearby middle school (student population: 702 in grades 5-8) were also reported to have cough illness suggestive of pertussis. On November 20, MDPH initiated an investigation in these schools and the surrounding community.

MDPH staff conducted active surveillance and case investigation in the high school from November 20 through January 4 and in the middle school from November 30 through January 5. Students with a persistent cough of at least 1 week's duration were identified by school officials and were interviewed by MDPH staff.

A clinical case of pertussis was defined as cough illness lasting 14 days or longer with onset during September 1-December 31. Persons with acute cough and from whom Bordetella pertussis was isolated from the nasopharynx were considered to have laboratory-confirmed cases. The MSLI also provided serologic testing of IgG antibody to PT by enzyme-linked immunosorbent assay. A positive test was defined as a level greater than or equal to 20.0 ug/mL in a single specimen obtained 14-56 days after onset of cough illness in a person aged greater than or equal to 11 years. Of those with a positive serologic test, only persons who also met the clinical case definition were included in the analysis.

A total of 225 cases of pertussis was identified among persons within the community; of these, 54 had a nasopharyngeal culture performed within 21 days of cough onset, and six were positive. In 20 other case-patients, serologic testing for pertussis was positive. The ages of case-patients ranged from 5 months to 46 years (median: 15 years).

Of the 225 total case-patients, 218 (97%) were enrolled in the school system, and 214 (95%) were aged 10-19 years. Peak onset of cough occurred from October 13 through November 30 (Figure 1). Paroxysmal cough was reported in 144 (64%) patients, whooping in 79 (35%), and posttussive vomiting in 56 (25%); at least one of these three symptoms was reported in 155 (69%) patients. No patients were hospitalized; 215 (96%) reported treatment with antibiotics, usually erythromycin.

Grade-specific attack rates at the high school were 27.9% among students in the 9th grade; 26.4%, 10th; 21.6%, 11th; and 19.2%, 12th. Attack rates in the middle school were higher among students in grades 7 and 8 (12.3% and 15.6%, respectively) than among those in grades 5 and 6 (4.9% and 5.6%, respectively). Duration of cough ranged from 10 to 95 days (median: 30 days). Cough illness among high school students peaked from October 20 through November 11 and among middle school students from October 27 through November 30. Review of vaccination records indicated that 209 (96%) students had received four or more doses of pertussis-containing vaccine. Most vaccine received was manufactured by the Biologic Laboratories at MDPH.

In an attempt to prevent further transmission within the schools, the MDPH recommended erythromycin prophylaxis for all high school students and staff on November 24, and for all students in grades 7 and 8 on December 14. Maryland

On November 16, 1992, a case of culture-confirmed pertussis in a 10-year-old elementary school student was reported to the Maryland State Department of Health and Mental Hygiene; onset of cough was October 31. During November 16-18, a letter was sent to parents of children who attended 5th grade at the elementary school and/or who shared a bus with the student, and surveillance was enhanced for additional cases. A clinical case of pertussis was defined as a cough lasting 14 or more days with onset during October 1-December 15 and at least one of the following symptoms: 1) paroxysms of coughing, 2) inspiratory whoop, or 3) posttussive vomiting, without other apparent cause.

Four confirmed cases of pertussis were identified: three among students with culture-confirmed pertussis and one in their 42-year-old teacher. These four persons had contact with each other only in the school setting.

Of 11 household or close personal contacts of the four case-patients, 10 received erythromycin prophylaxis; prophylaxis was not recommended for or given to classroom or school contacts. All 22 students in the classroom had received four or more doses of pertussis vaccine before age 6 years. Surveillance at the only medical facility serving the community identified six additional persons with cough onset from November 1 through November 25. All were negative by culture and direct fluorescent antibody testing when tested 3-23 days after onset, and none were epidemiologically linked to confirmed cases.

Reported by: S Lett, MD, J Thompson-Allen, Div of Epidemiology, H George, PhD, Massachusetts State Laboratory Institute, A DeMaria, Jr, MD, State Epidemiologist, Massachusetts Dept of Public Health. J Long, Kimbrough Army Community Hospital, H Dearborn, LS Majer, MD, Anne Arundel County Health Dept, Annapolis; K Williams, DM Dwyer, MD, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene. Div of Field Epidemiology, Epidemiology Program Office; Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; Div of Immunization, National Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Pertussis has rarely been documented in the United States as a cause of large outbreaks of cough illness among adolescents and young adults (1,2). The findings of the investigation in Massachusetts suggest that pertussis may cause outbreaks among adolescents, although a contributing role for other respiratory agents (e.g., Mycoplasma pneumoniae, Chlamydia pneumoniae, or adenoviruses) could not be excluded. Approximately half of reported pertussis cases in the United States occur among infants aged less than 1 year; only 12% of cases occur among persons aged 10-19 years (3). In comparison, in Massachusetts during 1992, 9% of reported cases occurred among infants, and 78% among persons aged 10-19 years. Possible explanations for this difference include increased awareness by clinicians and public health officials of pertussis as an etiology of cough illness among adolescents and young adults and the availability of serologic testing for diagnosis of pertussis among persons aged greater than or equal to 11 years.

Laboratory diagnosis of pertussis is difficult, and pertussis often is not considered in the differential diagnosis of cough illness among adolescents and adults. Cultures for pertussis require special media and techniques and may be positive only during the first 2-3 weeks of illness (4). Because of the low sensitivity and variable specificity of direct fluorescent antibody testing of nasopharyngeal secretions (5), this method cannot be relied on as a criterion for laboratory confirmation. Except in Massachusetts, serologic testing for pertussis diagnosis is not widely available (6). The sensitivity and specificity of single convalescent serum specimens for pertussis diagnosis must be further evaluated and standardized.

Antimicrobial prophylaxis with erythromycin (or with trimethoprim-sulfamethox-azole if erythromycin is not well tolerated) is recommended for all household and other close contacts of persons with pertussis, regardless of their ages and vaccination status (7). Schoolwide prophylaxis has not been generally recommended; however, in Massachusetts, concerns about the high attack rate of cough illness in the high school prompted the mass use of antibiotics. Although peak onset of cough occurred 2 weeks before mass chemoprophylaxis was initiated, only three new pertussis cases were reported subsequently. In contrast, in Maryland, schoolwide transmission did not occur despite apparent transmission within a single 5th-grade classroom.

Vaccine-induced immunity may wane with time (8); this waning immunity may have accounted for the higher attack rates among the high school students than among the middle school students in Massachusetts. The findings of these investigations underscore that pertussis should be considered in the differential diagnosis of prolonged cough illness among older children, adolescents, and adults -- regardless of reported childhood vaccination status. These groups may serve as a reservoir for spread of infection to infants and young children, in whom complications and long-term sequelae can be severe (9). The early recognition and treatment of pertussis among persons in older age groups may reduce transmission of infection to young or susceptible children. New acellular pertussis vaccines that are immunogenic in adults and less reactogenic than whole-cell pertussis vaccines (10) also require further evaluation for use among adolescent populations.


  1. Wassilak S, Smith G, Garbe P, Burstyn D, Manclark C, Orenstein

Pertussis outbreak in Colorado: use of newly-developed diagnostic test. In: Proceedings of the 18th Immunization Conference. Atlanta: May 16-19, 1983:37-41.

2. Mink C, Sirota N, Nugent S. An outbreak of pertussis in a fully immunized 8th grade class {Abstract no. 1730}. Program and abstracts of the 32nd Interscience Conference on Antimicrobial Agents and Chemotherapy. Anaheim, California: October 11-14, 1992:399.

3. Davis SF, Strebel PM, Cochi SL, Zell ER, Hadler SC. Pertussis surveillance -- United States, 1989-1991. In: CDC surveillance summaries (December 11). MMWR 1992;41(no. SS-8):11-20.

4. Strebel PM, Cochi SL, Farizo KM, Payne BJ, Hanauer SD, Baughman AL. Pertussis in Missouri: evaluation of nasopharyngeal culture, direct fluorescent antibody testing, and clinical case definitions in the diagnosis of pertussis. Clin Infect Dis 1993;16:276-85.

5. Halperin SA, Bortolussi R, Wort AJ. Evaluation of culture, immunofluorescence and serology for the diagnosis of pertussis. J Clin Microbiol 1989;27:752-7.

6. Onorato IM, Wassilak SG. Laboratory diagnosis of pertussis: the state of the art. Pediatr Infect Dis J 1987;6:145-51.

7. ACIP. Diphtheria, tetanus, and pertussis: recommendations for vaccine use and other preventive measures -- recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-10).

8. Mortimer EA Jr. Pertussis vaccine. In: Plotkin SA, Mortimer EA Jr, eds. Vaccines. Philadelphia: WB Saunders, 1988:74-97.

9. Nelson JD. The changing epidemiology of pertussis in young infants: the role of adults as reservoirs of infection. Am J Dis Child 1978;132:371-3. 10. Edwards KM, Decker MD, Graham BS, Mezzatesta J, Scott J, Hackell J. Adult immunization with acellular pertussis vaccine. JAMA 1993;269:53-6.

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