Pertussis outbreak in an elementary school with high vaccination coverage

BACKGROUND

An outbreak of pertussis in a US elementary school with high vaccination coverage was investigated to evaluate vaccine effectiveness and to identify potential contributing factors.

METHODS

Survey and cohort study of all 215 students of an elementary school (including 36 case patients) and 16 secondary cases among contacts.

RESULTS

Fifty-two pertussis cases were identified (attack rate among students, 17%). Receipt of <3 doses of pertussis-containing-vaccine compared with receipt of complete vaccination series was a significant risk factor for pertussis [relative risk, 5.1; 95% confidence interval (CI), 3 to 8.6]. The effectiveness of the complete vaccination series was 80% (95% CI 66 to 88). No evidence of waning immunity among students was found. The following contributing factors for the outbreak were identified: multiple introductions of pertussis from the community; delays in identification and treatment of early cases; and high contact rates among students. Antimicrobial treatment initiated >14 days after cough onset was associated with increased risk of further transmission of pertussis (relative risk, 10.1; 95% CI 1.5 to 70.3) compared with treatment within 14 days of onset.

CONCLUSIONS

This investigation demonstrated the potential for pertussis outbreaks to occur in well-vaccinated elementary school populations. Aggressive efforts to identify cases and contacts and timely antimicrobial treatment can limit spread of pertussis in similar settings. High vaccination coverage should be maintained, because vaccination significantly reduces the risk of the disease throughout the elementary school years, and to ensure timely diagnosis and treatment health care providers should maintain a high index of suspicion for pertussis among elementary school age children.

Epidemiology of diphtheria in South Dakota

Respiratory diphtheria was one of the most common causes of death among children in the pre-vaccine era. Since the introduction of diphtheria toxoid vaccine in 1920s, and its widespread use by the late 1940s, diphtheria became increasingly rare in the United States. However, through the 1970s diphtheria remained endemic in some states, with reported incidence rates > 1.0 per million population in six states (Alaska, Arizona, Montana, New Mexico, South Dakota, and Washington). Starting in 1980, less than five cases have been reported each year in the United States. The majority of culture-confirmed cases have been associated with importation from other countries. Toxigenic Corynebacterium diphtheriae, the organism causing diphtheria, was thought to have become rare or even have disappeared from previously endemic areas such as South Dakota. However, during four months in 1996, 11 persons (one index case, six patients and four household contacts) in an American Indian community in South Dakota were found to be infected by C. diphtheriae; six of these isolates were toxigenic. The findings in this report indicate that despite 20 years without reported respiratory diphtheria cases, toxigenic C. diphtheriae is still present in South Dakota. The continuous circulation of toxigenic strains of C. diphtheriae emphasizes the need for health care providers throughout South Dakota to promote timely vaccination against diphtheria among persons of all ages and ethnic groups, to be aware of the clinical signs and symptoms of diphtheria so that cases can be promptly diagnosed and treated, and further public health measures can be taken to contain this serious disease.

How many doses of diphtheria toxoid are required for protection in adults? Results of a case-control study among 40- to 49-year-old adults in the Russian Federation

During the Russian diphtheria epidemic of the 1990s, adults had an unexpectedly high rate of disease. A retrospective, matched case-control study was done to measure the effectiveness of one, two, or three or more doses of diphtheria toxoid against diphtheria among 40- to 49-year-old Russians. Thirty-nine diphtheria case-patients and 117 controls were studied. Previous vaccinations were included if one dose was received within the previous 10 years. Five cases (13%) and 33 controls (28%) had received three or more doses of vaccine. The matched odds ratio was 0.3 (95% confidence interval, 0.1-0.9) for three or more doses compared with no doses, which was a vaccine effectiveness of 70% (95% confidence interval, 10-90). A trend existed toward milder disease with increasing doses (chi2 test for trend, P=.02). The results suggest that Russian adults, who were unlikely to have acquired immunity to diphtheria through immunization or natural infection, required at least three doses of diphtheria toxoid for reliable protection against disease.