Contribution of Contact Sampling in Increasing Sensitivity of Poliovirus Detection During A Polio Outbreak—Somalia, 2013

Abstract

Background. In May 2013, a wild poliovirus type 1 (WPV1) outbreak reported in Somalia provided an opportunity to examine the contribution of testing contacts to WPV detection.Methods. We reviewed acute flaccid paralysis (AFP) case-patients and linked contacts reported in the Somalia Surveillance Database from May 9 to December 31, 2013. We restricted our analysis to AFP case-patients that had ≥3 contacts and calculated the contribution of each contact to case detection.Results. Among 546 AFP cases identified, 328 AFP cases had ≥3 contacts. Among the 328 AFP cases with ≥3 contacts, 93 WPV1 cases were detected: 58 cases (62%; 95% confidence interval [CI], 52%–72%) were detected through testing stool specimens from AFP case-patients; and 35 cases (38%; 95% CI, 28%–48%) were detected through testing stool specimens from contacts, including 19 cases (20%; 95% CI, 14%–30%) from the first contact, 11 cases (12%; 95% CI, 7%–20%) from the second contact, and 5 cases (5%; 95% CI, 2%–12%) from the third contact. Among the 103 AFP cases with ≥4 contacts, 3 (6%; 95% CI, 2%–16%) of 52 WPV1 cases were detected by testing the fourth contact. No additional WPV1 cases were detected by testing >4 contacts.Conclusions. Stool specimens from 3 to 4 contacts of persons with AFP during polio outbreaks are needed to maximize detection of WPV cases.

The critical role of acute flaccid paralysis surveillance in the Global Polio Eradication Initiative

“…16 Other supplementary methods to increase the sensitivity of surveillance include the collection of stool specimens from healthy direct contacts of AFP cases and/or from nearby communities, particularly when specimen collection from the index case is delayed beyond two weeks after the onset of paralysis. 17 If poliovirus is isolated from a direct contact of a virusnegative AFP case, a scenario which does occur several times each year in the remaining infected areas, the index case is confirmed as polio. Also, in areas with low surveillance quality, or whenever surveillance needs to be enhanced such as following the detection of a new outbreak, national programmes may conduct special 'AFP case search activities' during supplementary immunization campaigns, or by visiting health facilities and conducting retrospective record searches.…”