WASHINGTON — Wisconsin health authorities were able to put a stop to a spiraling outbreak of pertussis by advocating faster testing and use of antibiotics in all suspect cases, a state health department official reported at the National Immunization Conference sponsored by the Centers for Disease Control and Prevention.
Jeffrey Davis, M.D., of the Wisconsin Division of Public Health, gave the details of the epidemic, which lasted from May 2003 until February 2004 and occurred primarily in Fond du Lac County. In the 5 years before the outbreak, there had only been five cases of pertussis in Wisconsin.
Cases were defined using the Centers for Disease Control and Prevention's (CDC) definition of pertussis: a cough illness lasting more than 2 weeks with paroxysms, whoop, or posttussive vomiting. Cases were confirmed through patient follow-up interviews and/or lab confirmation by isolating Bordetella pertussis in culture, or through a positive polymerase chain reaction (PCR) assay.
During the outbreak, there were 313 cases reported in the county (in a total population of 97,296); 193 were confirmed in the lab, and 120 were confirmed by epidemiology. Just over half the cases were in females, and the median age was 14 years. Of those with confirmed pertussis, 70% were aged 10-19 years; 43% were aged 10-14 years. The incidence rate exceeded 1,000 per 100,000 in that younger cohort, said Dr. Davis.
After investigating, the health department determined that the outbreak probably started with two unvaccinated adolescents using a high school weight room. Of the initial 53 cases, 55% were linked to that weight room, said Dr. Davis.
During the epidemic's initial peak in mid-October, the health department alerted physicians to keep a close eye on potential cases. As the number of new cases continued to rise into November, the department issued another alert, suggesting more testing and use of antibiotics in any suspect cases.
That alert led to a sharp decline in cases, said Dr. Davis. During the first peak, it took a median of 10.5 days between the onset of cough and initiation of antibiotics. By the last peak, medication was generally started within 4 days of cough onset.
More than 5,000 courses of antibiotics were dispensed; 90% of the prescriptions were for azithromycin.
As physicians became more aware, they stepped up reporting, also, said Dr. Davis.
And PCR testing by the health department allowed for a rapid response—results were generally back to physicians within 24-48 hours.