Lessons learned from identifying clusters of severe acute respiratory
infections with influenza sentinel surveillance, Bangladesh, 2009--2020
Abstract
Background We explored whether hospital-based surveillance is useful in
detecting severe acute respiratory infection (SARI) clusters and how
often these events result in outbreak investigation and community
mitigation. Methods During May 2009– December 2020, physicians at 14
sentinel hospitals prospectively identified SARI clusters (i.e., ≥2 SARI
cases who developed symptoms ≤10 days of each other and lived
<30 minute walk or <3 km from each other).
Oropharyngeal and nasopharyngeal swabs were tested for influenza and
other respiratory viruses by rRT-PCR. We describe the demographic of
persons within clusters, laboratory results, and outbreak
investigations. Results Physicians identified 464 clusters comprising
1,427 SARI cases (range 0–13 clusters per month). Sixty percent of
clusters had three, 23% had 2, and 17% had ≥4 cases. Their median age
was 2 years (interquartile [IQR] 0.4–25) and 63% were male.
Laboratory results were available for the 464 clusters a median 9 days
(IQR = 6–13 days) after cluster identification. Less than one in five
clusters had cases that tested positive for the same virus: RSV in 58
(13%), influenza viruses in 24 (5%), HMPV in 5 (1%), HPIV in 3
(0.6%), adenovirus in 2 (0.4%). While 102/464 (22%) had poultry
exposure, none tested positive for influenza A(H5N1) or A(H7N9). None of
the 464 clusters led to field deployments for outbreak response.
Conclusions For 11 years, none of the hundreds of identified clusters
led to emergency response. The value of this event-based surveillance
might be improved by seeking larger clusters, with stronger
epidemiologic ties or decedents.