Current Trends Pertussis Surveillance -- United States, 1986-1988

During 1986-1988, state health departments reported 10,468 pertussis cases to the MMWR (4195 in 1986, 2823 in 1987, and 3450 in 1988), for an average crude annual incidence rate of 1.4 cases per 100,000 population (1.7, 1.2, and 1.4 in 1986, 1987, and 1988, respectively). The average incidence represents a 17% increase over that for 1984 and 1985 (1.2 per 100,000). Age-specific incidence rates were highest among children less than 1 year of age and declined with increasing age (Figure 1). Pertussis cases were reported from all 50 states and the District of Columbia; the highest average annual incidence rates were reported in Idaho (17.1 per 100,000), Kansas (17.0 per 100,000), Delaware (12.5 per 100,000), Hawaii (10.7 per 100,000), and New Hampshire (6.6 per 100,000), each of which reported one large outbreak during the 3-year period.

Supplemental detailed case reports on 8682 (83%) patients were received through the Supplemental Pertussis Surveillance System (SPSS).* The age distribution of these patients was similar to that of patients reported to the MMWR (Table 1, page 64). The following data are from the SPSS.

Of the 8682 patients, 2345 (27%) had culture-confirmed pertussis; 6125 (71%) had cough for greater than or equal to 14 days and/or had culture confirmation of pertussis. In early 1988, the Council of State and Territorial Epidemiologists (CSTE) approved clinical case definitions for uniform reporting of outbreak-related and sporadic pertussis cases: in an outbreak, a cough illness lasting greater than or equal to 14 days is considered a case; a sporadic case includes this criterion and paroxysms, whoop, or post-tussive vomiting. These case definitions, however, have not yet been implemented by all states. Overall, of 6000 patients for whom cough duration was known, 81% were reported to have had cough for greater than or equal to 14 days; this proportion was the same for patients with and without culture confirmation. Direct fluorescent antibody (DFA) testing of nasopharyngeal secretions was reported for 6449 (74%) patients. Of 4426 patients for whom cough duration was known, the clinical case definition of cough for greater than or equal to 14 days was met by 73% of those with a positive DFA test without culture confirmation and by 89% of those with a negative DFA test.

Percentages of hospitalization and complications (e.g., pneumonia, seizures, and encephalopathy) were highest for children less than 6 months of age and tended to decline with increasing age (Table 2, page 64). Of the 26 (0.3%) patients who died, 14 were less than 6 months of age (case-fatality rate in this group: 0.5%).

Based on the Immunization Practices Advisory Committee (ACIP) recommendations, children are appropriately immunized if they have received one dose of diphtheria and tetanus toxoids and pertussis vaccine (DTP) by 3 months of age, two doses by 5 months of age, three doses by 7 months of age, and four doses by 19 months of age (1). Of 3793 patients aged 3 months through 4 years with known vaccination status, 63% were not appropriately immunized; 34% had not received any doses.

Of the 8373 persons for whom information on therapy was available, 85% had received erythromycin, which is recommended by the ACIP. Of 5178 patients for whom initial date of therapy was known, 36% started therapy within 7 days after cough onset; 65% within 14 days; and 80% within 21 days. Of 5743 patients for whom duration of therapy was known, 51% completed the recommended 14-day course of erythromycin. Reported by: State and territorial epidemiologists. Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The increase in incidence of reported pertussis in 1986--especially among older children (Figure 1)--may be explained in part by an outbreak that occurred in Kansas in that year. The Kansas outbreak was the largest reported in the United States in the last 10 years and accounted for 1030 cases (31% of all cases reported to the SPSS in 1986). In this outbreak, an unusually large proportion (63%) of reported cases occurred in children 5-9 years of age. Only 4% of cases were confirmed by culture; 87% of patients had a positive DFA test without culture confirmation. Cough duration of greater than or equal to 14 days was reported for 107 (40%) of 268 patients for whom cough duration was known.

For 1987 and 1988, the age-specific incidence rates were similar to those for 1984 and 1985. From 1986 through 1988, as in previous years, infants were at highest risk for pertussis and pertussis-associated complications. Two thirds of the pertussis cases reported during that period in children aged 7 months to 4 years could potentially have been prevented by age-appropriate vaccination.

Erythromycin, recommended for patients with clinical pertussis and for selected contacts of pertussis patients, decreases infectivity and may limit secondary spread (1). Secondary spread of pertussis in households and on wards in a facility for persons with developmental disabilities has been attributed to an approximate 14-day delay between cough onset and initiation of erythromycin therapy and/or prophylaxis in the patients with primary cases (2-4).

An estimated 5%-10% of pertussis cases in the United States are reported to CDC each year (5); reporting is disproportionately greater for hospitalized patients with classical, laboratory-confirmed, and hence, more severe, cases. Diagnostic limitations restrict assessment of the full public health impact of pertussis. The routinely available methods for laboratory diagnosis of pertussis are culture and DFA testing of nasopharyngeal secretions. Culture of Bordetella pertussis is specific as a diagnostic test but may be insensitive (6); it is most useful for confirming the presence of B. pertussis in the community. Culture of B. pertussis is particularly insensitive when specimens are obtained late in the course of the illness (7) or from persons who have been treated with antimicrobials effective against B. pertussis (erythromycin, trimethoprim-sulfamethoxazole, or tetracycline) (8). Thus, negative culture results may be misleading. Because DFA testing for pertussis has been shown in some studies to have low sensitivity (18%) (6), variable specificity (9), and a positive predictive value of 56% (6), it should not be relied on for diagnosing and reporting pertussis. DFA testing was performed on nearly three fourths of patients reported to the SPSS, but a positive test did not predict the presence of cough for greater than or equal to 14 days.

Cough for greater than or equal to 14 days was relatively sensitive (84%) and specific (63%) for identifying patients with a positive pertussis culture during outbreaks in 1985 and 1986. Based on pertussis serology as the diagnostic standard, this case definition was 91% sensitive and 90% specific (10). Thus, clinical criteria may be especially useful when cultures are not obtained or when culture results are negative.

In a 1984 survey of state and territorial epidemiologists (11), 42% employed a case definition for pertussis; however, the case definitions varied widely. Forty-one percent counted cases of physician-reported pertussis if laboratory studies were negative; 51% counted physician-reported pertussis if laboratory studies were not done. With such reporting practices, many patients meeting the CSTE case definitions may go unreported if laboratory tests are negative or not done.

Newer serologic tests for pertussis are being developed (6,7) but are not yet available for routine use. In the interim, judicious use of laboratory tests, combined with standard clinical criteria, should improve the uniformity, completeness, and specificity of pertussis reporting.

References

1. ACIP. Diphtheria, tetanus, and pertussis: guidelines for

vaccine prophylaxis and other preventive measures. MMWR 1985;34:405-14,419-26.

2. Sprauer MA, Cochi SL, Patriarca PA, et al. Use of erythromycin in preventing secondary transmission of pertussis (Abstract). In: Program and abstracts of the twenty-ninth Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1989:199.

3. Biellik RJ, Patriarca PA, Mullen JR, et al. Risk factors for community- and household-acquired pertussis during a large-scale outbreak in central Wisconsin. J Infect Dis 1988;157:1134-41.

4. Steketee RW, Wassilak SGF, Adkins WN, et al. Evidence for a high attack rate and efficacy of erythromycin prophylaxis in a pertussis outbreak in a facility for the developmentally disabled. J Infect Dis 1988;157:434-40.

5. Hinman AR, Koplan JP. Pertussis and pertussis vaccine: reanalysis of benefits, risks, and costs. JAMA 1984;251:3109-13.

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

7. Steketee RW, Burstyn DG, Wassilak SG, et al. A comparison of laboratory and clinical methods for diagnosing pertussis in an outbreak in a facility for the developmentally disabled. J Infect Dis 1988;157:441-9.

8. Cherry JD, Brunell PA, Golden GS, et al. Report of the Task Force on Pertussis and Pertussis Immunization--1988. Pediatrics 1988;81:S939-84.

9. Broome CV, Fraser DW, English WJ. Pertussis--diagnostic methods and surveillance. In: Manclark CR, Hill JC, eds. International Symposium on Pertussis. Bethesda, Maryland: National Institutes of Health, 1978:19-22. 10. Patriarca PA, Biellik RJ, Sanden G, et al. Sensitivity and specificity of clinical case definitions for pertussis. Am J Public Health 1988;78:833-6. 11. Sacks JJ. Utilization of case definitions and laboratory reporting in the surveillance of notifiable communicable diseases in the United States. Am J Public Health 1985;75:1420-3. *Pertussis reports are submitted to CDC using two separate reporting mechanisms. The MMWR system includes basic demographic and disease occurrence information, which is the same for all diseases reported. MMWR cases are compiled by date of report. In the SPSS, introduced in 1979, reports on pertussis cases are submitted to CDC by state health departments. The reports contain more complete disease-specific information on age, sex, vaccination status, date of onset, clinical symptoms and signs, complications, and results of laboratory tests. SPSS cases are compiled by date of onset.

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