Despite successful vaccination programs, overall incidence of pertussis increased in the US during 2000-2016, especially among infants, a recent study found. Researchers used national surveillance data to describe pertussis epidemiology, including patient demographic characteristics, geographic distribution, and temporal trends. Cases reported through the National Notifiable Diseases Surveillance System between January 1, 2000 and December 31, 2016 were included. Average annual incidence was calculated overall, and by age and geographic subgroup. Among the findings:
- 339,420 pertussis cases were reported during the study period.
- Infants had the highest incidence (75.3/100,000 population), accounting for 88.8% of deaths.
- The majority of cases were in white (88.2%) and non-Hispanic (81.3%) persons.
- Nearly 10% of cases resulted in hospitalization and 0.1% were fatal.
- Differences existed by age.
- Incidence increased significantly over time, with baseline rates rising 1.7-fold between 2000-2008 and 2009-2016.
- Elevated case counts among persons aged 7-10 and 11-18 years coincided with the aging of acellular-primed birth cohorts.
- Incidence varied by geographic region.
Skoff TH, Hadler S, Hariri S. The epidemiology of nationally reported pertussis in the United States, 2000–2016. [Published online ahead of print August 30, 2018]. Clin Infect Dis. doi:10.1093/cid/ciy757.
I think the increase found in this study has many different factors that need to be taken into account. First, going back to the start of the study, Bordatella pertussis was bacteria that was very hard to grow in a lab. Over the period of this study, better methods of detection have been developed. This would have led to an increase in cases. With the advent of the Tdap vaccine, there has been more awareness of pertussis as a disease. Prior to vaccinating adolescents and adults, a paper in Pediatrics 2005 projected 800,000 to 3,300,000 cases of pertussis annually in the US. On the other hand, there are more vaccine refusers now than 18 years ago and the whole cell vaccine may have been more effective than the acellular vaccine. — John Russell, MD
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