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Passive surveillance fails to detect pertussis in adults, older children
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Passive surveillance may be associated with failure to detect symptomatic pertussis, particularly among adults and adolescents.
These findings suggest that providing clinics with free, rapid laboratory diagnostic testing, along with improved monitoring of household contacts, is needed for better detection of existing cases, the researchers wrote.
In a prospective, population based study, researchers identified all clinically suspected cases of pertussis in Catalonia and Navarre, Spain, that were reported to the country’s Regional Surveillance Units between January 2012 and December 2013. A confirmed case was defined as meeting the clinical definition and being either laboratory-confirmed by PCR or culture or epidemiologically linked to a PCR-confirmed case.
Cases that met the clinical case definition were reported to the appropriate surveillance unit, and an investigation was initiated to evaluate any possible additional cases within the same family unit. The researchers defined cases detected by passive surveillance as confirmed cases that were reported to a surveillance unit. Cases detected by enhanced surveillance were defined as those detected among family/household contact through follow-up investigation of passively reported cases.
For all confirmed cases, the researchers documented the following variables: age, gender, clinical symptoms, laboratory results and vaccination status. The researchers analyzed associations between these variables and the type of surveillance used for detection, and these were expressed as ORs and 95% CIs. Adjusted ORs were calculated using logistic regression to adjust for possible confounders.
The researchers found that 668 cases were identified through passive surveillance reports; as a result of these, 2,873 household contacts were investigated, leading to the detection of 456 additional cases. Passive surveillance was found to be the most prevalent means of detection for children under 18 years of age, and accounted for 95.7% of cases among children aged < 1 year. Moreover, among children between the ages of 5 and 10 years, 67.5% of the cases identified in the study were detected through passive surveillance.
However, among patients aged ≥ 18 years, enhanced surveillance was the most prevalent source of case detection (82.5%).
The researchers found that without investigating the household contacts of the confirmed cases, the researchers would have missed 456 cases (40% of all cases detected in the study). Moreover, enhanced surveillance identified 83 cases in children aged five to ten years and an additional 38 cases in children aged 11-17 years.
According to the researchers, adolescents and adults with mild or undetected atypical disease are known sources of B. pertussis transmission to infants and young children.
“However, the importance of enhanced surveillance is not limited to adults and adolescents but, as several authors have reported, some cases of pertussis in children are not reported,” the researchers wrote. “The underreporting of cases in children 1-10 years of age shown by our results should be taken into account in correctly estimating the incidence of pertussis and deciding on the best immunization strategies for its control in developed countries.” – by Jennifer Byrne
Disclosure: The researchers report no relevant financial disclosures.
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