Using an Outbreak in Rural Texas to Describe the Resurgence of Pertussis

BACKGROUND:   In recent years, the United States has experienced an increase in the reported numbers of illnesses and outbreaks of pertussis. The majority of the increase has occurred among infants and children 7-10 years of age, including those previously vaccinated. Several reasons have been provided for this including: waning immunity after last vaccine dose, symptomatic adults around susceptible children and questionable potency of the administered vaccines. In the fall of 2012, there was an outbreak of pertussis in a rural Texas county involving a school district. The age profile and the adequate vaccination status of cases in this outbreak is similar to what is been seen nationally with the resurgence of pertussis. This raises concerns, and calls for scrutiny in the entire process of vaccine delivery; vaccine efficacy, transport, storage, potency at delivery and vaccine scheduling.

METHODS:   Between October 24, 2012 and December 24, 2012, we interviewed the initial reported case, and used contact tracing to identify and then interview additional ill persons. We collected information on symptoms, exposures, close healthy contacts, vaccination status and medical intervention. Vaccine administration audits were conducted on the students and their institutions to ascertain coverage.

RESULTS:   Thirty-four cases were associated with this outbreak; 23 were PCR confirmed and 11 were epidemiologically linked. Ages ranged from 5 months-12 years, mean 8.21, median 9.5 and mode 10 years. The majority (62%) was between the ages of 7-10 years; Males were 43% and females 57%. Eleven cases were in 4 elementary schools and 18 cases in an intermediate school in the same school district, 2 in a daycare and 3 in homes. All cases had vaccination status up to date. Seventy-eight healthy close contacts were identified. The vaccine administration audits in the affected institutions revealed an overall coverage of over 90%.

CONCLUSIONS:   This outbreak report supports the national trend in recent pertussis resurgence in terms of the age group and vaccination status of affected cases. These findings underscore the need for improvement in the prevention effort of this vaccine preventable disease. The entire chain of vaccine delivery from manufacturer to administration needs proper scrutiny and monitoring to ensure safe and potent vaccines are administered. Genetic variations in Bordetella pertussis and other Bordetella species causing similar illness need to be identified and possibly incorporated into the vaccine. There is need for serologic studies to help determine the type, variations and fluctuation in protective antibody levels to better guide vaccine production and scheduling.