What is the prevalence of pertussis (whooping cough) in adults?

Prevalence of Pertussis in Adults

Pertussis is substantially more common in adults than passive surveillance suggests, with prospective studies demonstrating that 1-2 per 1,000 adults develop symptomatic pertussis annually, and serologic studies showing that 12-26% of adults with prolonged cough illness have evidence of B. pertussis infection. 1, 2

Epidemiologic Data from Surveillance and Prospective Studies

Annual Incidence Rates

• Prospective population-based studies estimate the annual incidence of symptomatic pertussis in adults aged 19-64 years ranges from 229-409 per 100,000 population, translating to approximately 299,000 to 626,000 cases annually in the United States 1
• The Minnesota HMO study found incidence rates of 229,375, and 409 per 100,000 for adults aged 20-29,30-39, and 40-49 years respectively 1
• These prospective data reveal that national passive surveillance captures only 1-2% of actual adult pertussis cases 1

Prevalence Among Adults with Cough Illness

• Among adults presenting with acute cough lasting ≥5 days who seek medical care, 8-26% have serologically confirmed B. pertussis infection 1
• In a Canadian multicenter study, 19.9% of adolescents and adults meeting criteria for postinfectious cough had confirmed pertussis 1
• Among adults with cough illness lasting ≥1-2 weeks, ≥12% have evidence of pertussis infection 2

Asymptomatic and Subclinical Infections

• The proportion of B. pertussis infections that are symptomatic ranges from 10-70%, depending on population and setting 1
• Among elderly adults living independently, 3.3-8% have pertussis infections annually, but only 37.5-50% of these are symptomatic 1
• A nationally representative U.S. sample found 2.9% prevalence of recent B. pertussis infection among persons aged 10-49 years 1

Household and Outbreak Attack Rates

Transmission Dynamics

• In households with a pertussis index case, the attack rate among adult contacts is 26.7% (84 of 265 adults), independent of whether a child or adult was the source 3
• During the 1962 Kent County outbreak, the attack rate among adults aged >20 years in affected households was 21% 1
• Adults are frequently the source of pertussis transmission to infants, accounting for 24% of identified sources when parents or grandparents had cough illness 1

Outbreak Settings

• In community outbreaks, 23-42% of cases occur among adults aged >20 years 1
• Teachers exposed to students with pertussis face approximately 4-fold higher risk compared to the general population during periods of high adolescent pertussis activity 1

Clinical Implications and Underdiagnosis

Healthcare Utilization

• Adults with pertussis make multiple medical visits: 31% had one visit, 31% had two visits, and 35% had three or more visits during their illness 1
• 78% of employed adults with pertussis miss work for a mean of 9.8 days, with 10-16% unable to work for more than 1 month 1

Diagnostic Challenges

• Pertussis is often not considered in the differential diagnosis of chronic cough by many practitioners, contributing to substantial underdiagnosis 1, 4
• The characteristic "whoop" is usually absent in adults, making clinical recognition difficult 1, 4
• Many adults present with only a nondistinct protracted cough as the sole manifestation 1

Key Clinical Pitfalls

• Waning immunity is universal: immunity from childhood vaccination or natural infection wanes within 5-20 years, making all adults susceptible to reinfection 1, 4, 3
• Adults serve as the primary reservoir for transmission to vulnerable infants, who account for 92% of pertussis deaths 1, 5
• The prolonged cough (typically >3 weeks, often lasting months) leads to extensive medical evaluations when pertussis is not considered 1
• Complications occur in adults more frequently than commonly perceived, including pneumonia (up to 5%), rib fractures (up to 4%), and hospitalization (up to 3%, or 12% in older adults) 1, 5