Pertussis -- Maryland, 1982

During 1982, 79 cases of pertussis were reported to the Maryland Department of Health and Mental Hygiene (1), a marked increase from the one to 18 cases reported annually during the previous 10 years. All cases were investigated. Thirty-five cases were from Baltimore city, and 44 were from 14 of the state's 23 counties. The first patient reported to have pertussis had onset in March. The number of cases peaked in July and August and decreased gradually through December (Figure 1).

Of the 79 reported cases, 32 occurred in males and 47 in females. Ages ranged from 7 weeks to 23 years. Sixty patients (76%) were less than 1 year of age (a pertussis incidence rate in Maryland of 0.22/1,000 children less than 1 year old), and forty-six (58%) were under 6 months of age (Figure 2).

Fifty-seven percent of all patients and 68% of patients less than 1 year old were hospitalized. The average duration of hospitalization was 8.6 days. Whoop was reported in 32 (41%) patients, episodes of apnea in 17 (22%), and pneumonia in 12 (15%), of whom 11 were under 1 year of age. Two (3%) of the 79 children, both infants, developed seizures; one of these (1/79) also developed an encephalopathy. No deaths occurred.

Forty-four cases (56%) were laboratory confirmed, 29 (37%) by direct fluorescent antibody (DFA) technique, four (5%) by culture, and 11 (14%) by both DFA and culture. The remaining thirty-five (44%) reported cases were diagnosed on clinical grounds alone. Twenty-three (52%) of the 44 hospitalized patients had laboratory-confirmed cases. Twenty-three (32%) of the 71 patients for whom laboratory specimens were submitted received antibiotics before the specimens were obtained; only seven (30%) of these were DFA- and/or culture-positive. By contrast, of the 48 patients whose specimens were taken before antibiotic administration, 35 (73%) were DFA- and/or culture-positive (p 0.01). For two patients, information on when antibiotics were begun was unavailable.

Of the 33 patients 6 months of age or older, 20 (61%) had received fewer than three doses of pertussis vaccine; these episodes may have been prevented by vaccination. Twenty-six (33%) of all patients were non-compliant with the age-recommended diphtheria-tetanus-pertussis (DTP) dosage schedule for the following reasons: illness at the time of scheduled vaccination--13 (50%), prematurity--three (12%), religious belief--three (12%), fear of vaccine effects--three (12%), and other--four (15%).

The household of each reported patient was investigated. In 72 completed household investigations, 236 household members were identified, of whom 74 (31%) were less than 10 years old. Immunization records were available for 64 (86%) of these children. Prior receipt of three or more doses of DTP vaccine was verified for 54 (84%). Four secondary cases were identified among all household contacts, one in an unimmunized child aged 4 years, two in children aged 20 months and 3 years with documentation of three or more doses of DTP, and one in an adult with an undocumented history of three doses of DTP as a child. Pertussis was laboratory-confirmed in the three secondary cases in children or in the primary case within their households. Although the numbers were small, the calculated clinical vaccine efficacy in household contacts 0-9 years of age in Maryland was 89%.

The increase in pertussis activity in 1982 was confirmed by reviews of hospital admissions and laboratory specimen submissions for 1981 and 1982. A survey of admissions for pertussis or pertussis-like syndromes to six major hospitals in the Baltimore metropolitan area revealed that, in 1981, only four children were admitted for pertussis--one with laboratory confirmation of disease. In contrast, in 1982, 25 children were hospitalized with pertussis--10 with laboratory confirmation. The Maryland State Laboratory received 161 specimens from patients with clinical pertussis for examination in 1981; three were DFA- or culture-positive. In 1982, the same laboratory, using the same procedures and personnel, received 324 specimens; 31 were DFA- or culture-positive. Many of the specimens submitted in 1982 were from contacts of patients.

While completion rates for DTP immunization were high at school entry (96%) in 1980 and 1981 in Maryland (2), completion rates in the preschool population may be considerably lower. In one comprehensive child-care clinic in Baltimore city, only 67 (69%) of the 97 infants 7.5-9.5 months of age on December 17, 1982, had received three doses of DTP vaccine.

Following a television presentation on pertussis vaccine side effects, DTP vaccine sales by one pharmaceutical company to the private medical sector in Maryland decreased 45% in April 1982, compared to average monthly sales for the preceding 3 months. Concomitantly, DT/Td* sales to the private medical sector increased 160%. Although DTP sales returned to normal during the following 2 months, DT/Td sales continued at 100% above the average of the first 3 months of 1982 through at least June 1982, the last month for which data are available. Following recognition of the increase in pertussis in Maryland, some private providers began to request pertussis single antigen vaccine from the state health department. Reported by Local health depts, FYC Lin, MD, M Johnson, RE Longenecker, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene; Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Despite high immunization levels of 96% for at least three doses of DTP vaccine in children entering school, Maryland experienced a marked increase in pertussis cases in 1982. Over 50% of pertussis patients were hospitalized for more than 1 week each; 18% of patients less than 1 year old developed pneumonia. Maryland's experience, as well as that of the United States from 1979 to 1981 (7), clearly indicates that pertussis remains a serious illness in young children.

Sixty-one percent of Maryland pertussis patients 6 months of age or older had not received three doses of DTP vaccine and can be considered as having had potentially vaccine-preventable cases (3). Three doses of pertussis vaccine generally provide a clinical vaccine efficacy between 63% and 94% (4-8). Furthermore, vaccine recipients who do develop disease have been shown to have decreased severity of illness, compared to that in patients who do not receive vaccine (4,7,9).

Age-specific immunization coverage of younger children, particularly those between 6 and 11 months of age, is not available nationwide. In Tennessee, where immunization status was obtained in 98% of a sample of 2-year old children, 91% had received three doses of DTP (10). In Hawaii, 68% of a younger cohort, aged 14 months, attending public health clinics had received three doses of DTP, which is comparable to the Baltimore clinic's experience of 69% in children 7.5-9.5 months of age (11).

Prevention measures against pertussis must stress full immunization of children at the earliest age possible. By ensuring the administration of three doses of DTP by 6 months of age, a fourth dose approximately 1 year later and a booster dose between 4 and 6 years of age, as recommended by the Immunization Practices Advisory Committee (ACIP) (3), the maximum obtainable age-appropriate, vaccine-induced protection can be ensured for children 6 months to 7 years old, thus both reducing the occurrence of pertussis in this age group and decreasing the exposure risk to pertussis organisms of infants less than 6 months of age.

Minor illnesses without fever, such as mild upper respiratory infections, should not cause postponement of vaccinations. However, scheduled DTP vaccination should be postponed for the duration of a severe febrile illness. In such instances, the health care provider should reschedule the child for DTP immunization at the earliest time possible and provide followup to assure the child returns for the missed dose.

The percentage of organism recovery is highest when specimens are obtained during the initial 3 weeks of illness and before antibiotics are instituted. Present laboratory procedures for Bordetella pertussis confirmation consist of culture and DFA techniques. Properly obtained and processed cultures can be more sensitive than DFA results; in addition, positive culture results are highly specific. Under favorable hospital conditions in which direct plating of the specimen is done, culture confirmation has been obtained in 87% of cases (12).

References

1. Lin FYC, Johnson M, Longenecker R, Israel E. Pertussis outbreak, Maryland 1982. Md State Med J 1983;32:343-6.

2. Maryland State Department of Health and Mental Hygiene. Results of school enterer assessments, 1981 and 1982.

3. CDC. Diphtheria, tetanus, and pertussis: guidelines for vaccine prophylaxis and other preventive measures. MMWR 1981;30:393-407.

4. Jenkinson D. Outbreak of whooping cough in general practice. Br Med J 1978;177:557-8.

5. Broome CV, Fraser DW. Pertussis in the United States, 1979: a look at vaccine efficacy. J Inf Dis. 1981;144:187-90.

6. Broome CV, Preblud SR, Bruner B, et al. Epidemiology of pertussis, Atlanta, 1977. J Peds. 1981;98:362-7.

7. CDC. Pertussis surveillance, 1979-81. MMWR 1982;31:333-6.

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