Highest rates of pertussis occur in infants <3 months of age, too young to be fully vaccinated. The 2012 national outbreak provided a valuable opportunity to study sources of infection for these infants at highest risk of severe complications and death.
Households of infants <3 months of age with laboratory-confirmed pertussis between August 2012 and October 2013 were invited to complete a questionnaire with information on household members’ demographics, relationship with the infant, chronology of cough onset where relevant and vaccination history. Contacts were also invited to provide an oral fluid sample for antipertussis toxin IgG testing. Individuals with laboratory evidence of infection and cough onset up to 3 months before infant onset were considered probable sources of infection.
In total, 220 contacts from 63 families were included in the analysis. In 86% of households (54/63), at least one positive result was found with 44% (97/220) of all contacts testing positive. Around 29% (31/108) of noncoughers tested positive. A probable source of infection was found for 46% (29/63) of infant cases. Mothers were the probable source in 38% of cases, followed by siblings (31%) and fathers (10%).
Household contacts play an important role in the transmission of pertussis to infants and when identified, mothers were the main sources of infection. Immunization during pregnancy has a key role in preventing infant disease through passive protection from birth and reduced maternal exposure.