In 1982 and 1983, 4,358 pertussis cases were reported to MMWR (1,895 in 1982; 2,463 in 1983). Individual case report forms* were received on 3,159 persons who had onset during this period, representing 72% of the total number of cases reported to MMWR. By contrast, in 1980 and 1981, report forms were received on 32% of the total cases reported to MMWR. Forms were received from 45 states and the District of Columbia during 1982 and 1983, compared to 40 states during 1980 and 1981. New York (540 forms), Oklahoma (347), Illinois (335), and Pennsylvania (322) submitted the largest number of forms, comprising 90% of cases reported by these states to MMWR and 49% of all individual case report forms received by CDC for persons with onset during 1982 and 1983. During late 1982 and early 1983, New York and Pennsylvania reported substantial localized outbreaks among members of certain religious groups that generally do not accept immunizations; during 1983, Oklahoma experienced a statewide outbreak (1).

In 1982 and 1983, the age distribution of cases reported to MMWR for which ages were known was similar to the cases for which report forms were received and on which ages were given, indicating the representativeness of the forms received (Table 2). Forty-three percent of persons for whom case report forms were received were under 6 months old. The crude incidence rate of reported pertussis in the United States in 1982 was 0.83 per 100,000 total population, and in 1983, 1.05/100,000. The incidence rate for children under 1 year old in 1982 was 27.2/100,000, and in 1983, 36.1/100,000.

The analyses below are limited to the 3,159 cases for which individual report forms were available. Pertussis was laboratory-confirmed in 2,154 (68%) of these cases; 9% of cases were confirmed by culture; 46%, by direct fluorescent antibody (DFA) testing of nasopharyngeal mucous smears; and 13%, by both culture and DFA.

Whoop was described in 50% of patients 0-5 months old, 57% of those 6-11 months old, 61% of those 1-4 years old, and 57% of those 5-9 years old. Apnea was present in 40% of patients under 1 year old. Pneumonia confirmed by x-ray occurred in 16% of reported patients (Table 3). X-ray-confirmed pneumonia was noted in 23% of patients under 6 months old, 17% of patients 6-11 months old, and 12% of patients 1-4 years old. Forty-nine percent of reported pertussis patients were hospitalized, including 77% of infants under 6 months old, 59% of those 6-11 months old, and 28% of those 1-4 years old. Seizures were reported in 59 (1.9%) of the 3,159 patients; 59% of patients with seizures were under 6 months old, and 76% were under 1 year old. Encephalopathy was reported for nine (0.3%) of the patients, eight of whom were under 1 year old. Fifteen deaths were reported, for an overall case-fatality ratio (CFR) of 0.5%. Thirteen of the deaths occurred in patients under 6 months of age, for a CFR in this age group of 1%. Nine of the deaths occurred in patients with pneumonia, one of whom was reported to have also had encephalopathy.

Based on age criteria derived from the current diphtheria-tetanus-pertussis (DTP) vaccine recommendations of the Immunization Practices Advisory Committee (ACIP),** 1,117 (68%) of the 1,637 reported patients 3 months to 6 years old with known vaccine status were not appropriately immunized with DTP vaccine (2). Sixty-six percent of 1,011 patients 7 months to 6 years old with known vaccine status had not received at least three doses of vaccine, the minimum number considered necessary for adequate vaccine protection against pertussis; 42% had not received any doses.

Information was available on 440 household contacts 6 months to 9 years old. Secondary attack rates were determined for unvaccinated household contacts (no DTP doses) and for household contacts who had received three or more DTP doses. Vaccine efficacy for three or more doses compared to no doses among household contacts 6 months to 9 years old was 91.4% (95% confidence limits 85.9, 94.5). Reported by Surveillance, Investigations, and Research Br, Data Management Br, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Earlier surveillance data indicated that pertussis had substantial health impact in the United States in terms of morbidity and complications, particularly in infants and young children, and that DTP vaccine provided a high level of protection against clinical disease (3). Nationwide pertussis surveillance data for 1982-1983 continue to confirm these findings.

Most reported pertussis cases among children under 7 years old occurred among those inadequately vaccinated for their age. Among patients 7 months to 6 years old, 66% had received fewer than three DTP doses; many of these cases may have been vaccine-preventable.

Data in the pertussis surveillance systems suffer from underreporting of cases and, therefore, the cases reported to both systems probably include a disproportionate number of hospitalized, laboratory-confirmed, and classical cases. Nonetheless, the data are useful for estimating minimum incidence rates, maximum complication risks, the health impact of pertussis, and the benefits of vaccine usage.

Pertussis vaccine is associated with frequent minor-to-moderate local and systemic reactions (4) and with rare, but serious, neurologic reactions (5). Recommendations from the ACIP and the American Academy of Pediatrics for routine use of DTP vaccine depend on the assessment of disease and vaccine risks and the benefits of the vaccine. A reevaluation of the benefits and risks of DTP vaccine and the risks of pertussis showed that 11.1 dollars in benefits were accrued for every dollar spent for a pertussis vaccination program (6). Following the recent rise in vaccine price, a recalculation using the current price showed a 3.1:1 benefit-cost ratio (7).

As of 1983, 27 states, through legislation, required four doses of DTP for school entry, and 13 states and the District of Columbia required three doses. One state required an unspecified number of doses for school entry. Nine states did not have school entry requirements for pertussis vaccine. In the 1983-1984 school year, an estimated 95% of children entering school in the United States had received at least three doses of DTP. Because of the continued high level of vaccine coverage among persons entering school and because of laws in 42 states and the District of Columbia that require DTP for entry into licensed day-care centers, the current risk of acquiring pertussis remains low. To further reduce the occurrence of pertussis and its health impact, efforts must be intensified to provide DTP to all children without specific contraindications to pertussis vaccine as soon as they become eligible for each dose of vaccine (2,8).

References

1. CDC. Pertussis outbreak--Oklahoma. MMWR 1984; 33:2-4, 9-10.

2. ACIP. Diphtheria, tetanus, and pertussis: guidelines for vaccine prophylaxis and other preventive measures. MMWR 1981;30:392-6, 401-7.

3. CDC. Pertussis surveillance, 1979-1981. MMWR 1982;31:333-6.

4. Cody CL, Baraff LJ, Cherry JD, Marcy SM, Manclark CR. Nature and rates of adverse reactions associated with DTP and DT immunizations in infants and children. Pediatrics 1981;68:650-60.

5. Miller DL, Alderslade R, Ross EM. Whooping cough and whooping cough vaccine. The risks and benefits debate. Epidemiologic Reviews 1982;4:1-24.

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

7. Hinman AR, Koplan JP. Pertussis and pertussis vaccine: further analysis of benefits, risks, and costs. Presented at the Fourth International Symposium on Pertussis. Geneva, Switzerland. September 20, 1984 (in press).

8. ACIP. Supplementary statement of contraindications to receipt of pertussis vaccine. MMWR 1984;33:169-71. *The occurrence of pertussis and its health impact are monitored by CDC. State health departments report pertussis cases weekly and the age distribution of cases annually to MMWR. Supplementary case report forms are submitted by state health departments on a portion of these cases. The forms contain information on age, sex, vaccine status, date of onset, symptoms, complications, and laboratory confirmation. In some instances, information is also received on household contacts of pertussis patients. **Appropriately immunized for age if received: one dose by 3 months of age; two doses by 5 months of age; three doses by 7 months of age; four doses by 19 months of age.

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