Bangladesh was declared polio-free, along with ten other WHO SEARO member countries, on 27th March 2014. Despite this important achievement, population movement means that the risk of poliovirus being imported from either of the two remaining polio endemic countries, Pakistan and Afghanistan, remains present.
In order to detect any cases of poliovirus that might occur, WHO carries out routine acute flaccid paralysis (AFP) surveillance activities in Bangladesh. In the absence of cases of paralysis, environmental surveillance can be carried out as a supplementary activity to gain additional information on low-grade circulation of poliovirus, including detection of vaccine-derived polio virus (VDPVs). This can help guide the polio programme in taking appropriate measures to contain any flagged situations that may be identified. Ad-hoc environmental surveillance, especially in polio-free regions, also provides insights into the international spread of poliovirus. Environmental surveillance usually involves testing sewage or other environmental samples for the presence of poliovirus.
In Bangladesh, environmental surveillance began in September 2015 by collecting samples from four sites in Dhaka, using the ‘grab’ method. At the time of writing, 52 samples had been collected from selected sewage pits and other sites in the Gulshan, Bashabo and Tongi areas. So far, 46 samples have been tested at the National Polio and Measles Laboratory (NPML), the only WHO accredited laboratory in the country. Preliminary results indicate no wild poliovirus circulation in Bangladesh.