Many places which have the resources will then do a full sequence on any +ve samples as well to determine whether there is community transmission since this will show up as a number of related viruses which are all related to each other more closely than they are to the parent strain.
London screening frequently sees unrelated OPV strains which are due to people who have recently been vaccinated with OPV in places where that is still the preferred vaccine, what is concerning here is that the deep sequencing shows that there appears to be some person to person spread of a vaccine derived strain.
To answer your question, this is a highly sensitive and extremely specific test. Details no doubt available in the open literature somewhere.
Bet that isn't discussed anywhere.
>The location and timing of poliomyelitis cases showed spatial and temporal variability. The sensitivity of AFP surveillance to detect serotype 1 poliovirus infection in a district and its neighbours per month was on average 30.0% (95% CI 24.8–35.8) and increased with the incidence of poliomyelitis cases. The average population sensitivity of a single environmental sample was 59.4% (95% CI 55.4–63.0), with significant variation in site-specific estimates (median varied from 33.3–79.2%). The combined population sensitivity of environmental and AFP surveillance in a given month was on average 98.1% (95% CI 97.2–98.7), assuming four samples per month for each site. https://link.springer.com/article/10.1186/s12879-018-3070-4
>Four quarterly visits were made to 78 ES sites in 21 states of Nigeria, and ES site characteristic data were matched to 1345 samples with an average enterovirus prevalence among sites of 68% (range, 9%–100%). A larger estimated catchment population, high total dissolved solids, and higher pH were associated with enterovirus detection. A random forests model predicted “good” sites (enterovirus prevalence >70%) from measured site characteristics with out-of-sample sensitivity and specificity of 75%. https://academic.oup.com/jid/article/225/8/1377/5818305?logi...
Other discussion of environmental surveillance for polio:
The vaccine used in the UK is not an attenuated virus. So this was “ imported”. The news is likely being circumspect due to concerns of profiling immigrants or refugees or religious communities most prevalent where this vaccine is used.
So far no cases have been found of transmission between people.
I would be interested to know the sensitivity of the test they are using.