Fig. 2From: The estimated incidence of pertussis in people aged 50 years old in the United States, 2006–2010Incidence* of cough illness attributed to B. pertussis by month (a) and by year (b). *Please note that as data were only collected for 9 months during 2006 in the current study, an annual figure was approximated by multiplying by 12/9Back to article page