Zooming In on Pertussis Epidemiology In the United States

BACKGROUND

Pertussis is the most poorly controlled bacterial vaccine-preventable disease in the U.S. Although incidence generally peaks every 3-5 years, regional variations in reported disease are common. In 2009-2010, several states described rates comparable to those during the 2004-2005 peak, while other states observed fewer cases than in recent years. Understanding regional differences in the epidemiology of pertussis is important for assessing the impact of vaccination programs and prevention and control strategies.

OBJECTIVES

To describe regional differences in the epidemiology of pertussis in the U.S. during 2009-2010.

METHODS

We analyzed pertussis cases reported through NNDSS as probable, confirmed and with unknown status between 2009-2010. Cases were grouped into nine MMWR geographic reporting regions. Overall and age-specific incidences were calculated using census data. Case-fatality ratios (CFR) and the proportion outbreak-related were calculated.

RESULTS

In 2009-2010 (provisional data), overall incidence was 12.43/100,000. Incidence differed by region, ranging from 5.58/100,000 (S Atlantic) to 25.80/100,000 (WN Central). By age group, infants <1 year had the highest incidence in each region (range: 55.73/100,000–247.15/100,000); 8 regions reported the second highest burden among 7-10 year olds (range: 19.68/ 100,000–137.18/100,000). Despite representing only 15% of the total U.S. population, the EN Central region contributed over 22% of cases. The highest CFR for infants <1 year was 12.13/1,000 cases (Pacific); no deaths were reported by New England. Over 25% of cases were reportedly associated with outbreaks; the proportion of outbreak-related cases was 14 times higher in the WN Central region (43%) compared to the Pacific (3%).

CONCLUSIONS

While regional differences in incidence were observed, geographic variability in circulation is unlikely the sole contributor. An improved understanding of regional variability is required to monitor changes in the epidemiology of pertussis in the U.S., as well as identify weaknesses in national reporting.