An eradicated form of familial polio emerged from routine sewage monitoring in the Netherlands last year, offering a cautionary tale of the importance of monitoring for the stubborn virus. researchers report this week in the Eurosurveilance magazine.
The sewage sample was positive for infectious poliovirus in mid-November and genome sequencing revealed a strain of wild-type poliovirus 3 that was infected Declared globally extinct in 2019. Its potential revival would be a devastating setback in decades of efforts to finally eradicate highly infectious and potentially crippling germs.
A little background: There are three types of wild poliovirus: Type 2 and Type 3 have been eradicated, with the former being eradicated in 2015. Wild poliovirus type 1 continues to circulate in Afghanistan and Pakistan. There are also occasional vaccine-derived polioviruses circulating in communities with low vaccination rates, as was the case recently in New York.
Last year’s positive wastewater sample was the first and only evidence of polio infection with the past strain in the Netherlands. It happened to an employee at a Bilthoven Biologicals vaccine manufacturing facility that makes inactivated polio vaccine. The Netherlands had set up routine wastewater monitoring around the production facility to monitor such a virus outbreak.
Genome sequencing made it clear that this was an active infection rather than a case where the virus was somehow dumped down the drain. The virus isolates showed two to three mutations, indicating human shedding. So officials worked to determine which employees had access to type 3 polio in the weeks leading up to the positive sample. They narrowed it down to 51 employees and tested blood and stool samples from each. Only one was positive.
How this employee got infected is unclear. The person was fully vaccinated against polio and had no symptoms. Still, they shed infectious virions of an otherwise eradicated virus in their stool that could potentially spread to others. Also, the person lived in a community with a immunization coverage rate of less than 90 percent.
On December 8, the employee agreed to self-isolate under daily supervision by local health workers. Bilthoven Biologicals housed its infected employee in an isolated home located in a community with more than 90 percent immunization coverage. Local health workers ensured the person was following strict hygiene measures while still shedding virus. The person’s feces were collected in a one-way system and burned. The person was only allowed to see people outside, without physical contact.
The infected employee spent the next 33 days in isolation, including over the holidays, until he had three consecutive negative stool samples. In total, the person shed the virus for 51 days. However, contact tracing and further staff testing revealed no evidence of other infections and sewage sampling revealed no other positive samples.
Overall, local health authorities stressed the importance of surveillance in this case. “This event demonstrates that incidents leading to containment breaches and even infection go unnoticed and can go unreported in the absence of routine monitoring,” they concluded.
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