The Final Frontier in the Fight Against Polio? Sewers
WHY YOU SHOULD CARE
Unless your sewers are polio free, you could still catch the disease.
Every week, Lucky Sangal and her team at the World Heath Organization in India put on masks and gloves, tie a rope to a bucket and throw it into a flowing sewage stream at seven designated sites in New Delhi. They then pull out the bucket, filter the wastewater through a fine mesh cloth and pour it into test bottles that are sent to a lab in refrigerated containers. About 15 days later, Sangal’s team gets a report listing everything found in the smelly sample, including bacteria that can cause common ailments from urinary tract infections to diarrhea. “All of those things that typically live in sewage are OK,” says Sangal, who oversees the sampling operation to prevent disease spread. “What we don’t want to see is polio.”
India was declared polio free six years ago. Spread by a virus, the crippling disease primarily afflicts young children by damaging the spinal cord and causing paralysis. Since 1988 when there were 350,000 recorded cases in 125 countries, the Global Polio Eradication Initiative (GPEI), the transnational project that has driven the planet’s fight against the disease, has reduced polio cases by 99.9 percent. After more than two decades of effort, India recorded its last polio case in January 2011.
But that doesn’t mean the threat has passed. The virus is still known to be circulating in Pakistan and Afghanistan, India’s neighbors, and infected travelers and migratory groups may bring it across the borders without even knowing — because in some cases polio doesn’t have symptoms. So how does one guess where the next outbreak may be brewing? The answer is sewage — the fermenting menagerie of pathogens simmering together — some excreted by humans or animals, and some naturally present in the environment. Even if an infected person doesn’t show symptoms, the polio virus replicates in their intestines and emerges in their feces.
We cannot in all sincerity say ‘we are polio free’ if we are not actively looking for it.
Tunji Funsho, Rotary International Nigeria
That’s why polio surveillance workers across India and other countries at the front lines of the fight against polio, such as Pakistan and Nigeria, are increasingly turning to sewage testing to catch the virus before it can spread again among populations thought to be safe.
“These days we don’t see it, which is good,” says Sangal, of the samples her team collects.
At a time when the world is battling the COVID-19 crisis, the strategy deployed by Sangal and her peers in India, Pakistan and Nigeria is also offering lessons for ways in which researchers can prepare for the long-term fight against the coronavirus. Already, 12 research teams around the world are plotting ways in which they can test wastewater years from now, when the current pandemic has faded, to ensure that the virus doesn’t return.
When they get down to work, the experiences of polio’s sewage warriors will offer them valuable guidance.
India has 53 collection sites in nine states, and more will join soon, says Pankaj Bhatnagar, deputy team lead at the country’s National Polio Surveillance program. Pakistan, which still has occasional polio outbreaks, operates 60 regular sampling sites and eight ad hoc ones, which were set up last September. Nigeria, which started with about 25 sites in 2010, now has 113, says Tunji Funsho, chair of the Nigeria PolioPlus Committee at Rotary International, a global nonprofit that’s part of the GPEI.
Usually, these collecting spots are set up at the catchments that drain sewage from urban slums — the mixing bowls of people and migratory populations that come and go, with some potentially harboring the infection. If a sample proves positive, health workers immediately immunize all young children in the area. After the virus is sequenced, scientists can effectively pinpoint its birthplace — and alert health authorities in that area to also immunize children.
Sangal’s samples are showing up negative now, but older generations in India remember how three decades ago, polio was endemic in the country, which was also the global capital of the disease. “In [the] early to mid-1980s, the entire world used to have 1,000 cases of polio every day, and India used to contribute 500 of them,” says Deepak Kapur, Funsho’s counterpart at Rotary in India.
And many decades before that, polio outbreaks paralyzed Europe and the U.S. In 1916, the U.S. recorded more than 27,000 polio cases, and 6,000 deaths. Then, in 1952, the virus hit the U.S. again, this time killing more than 3,000 children and infecting more than 60,000.
Unlike in India, seeing positive polio samples in sewage isn’t that unusual for Nosheen Safdar, divisional polio surveillance officer in Pakistan’s capital of Islamabad. Dressed in protective overalls and high rubber boots, her team members wade into sludge once a month. “All major cities, metropolises … all provinces have those sites,” Safdar says.
Testing samples from remote locations is challenging because they often don’t have labs nearby. Samples must reach labs within 72 hours “in good conditions with ice packs still frozen and no leakage,” says Safdar. For distant areas, samples are sent to a courier service that dispatches them to a lab in Islamabad, she adds.
But the evidence suggests that sewage testing works. Last July, sewage samples in seven neighborhoods of Pakistan’s largest city, Karachi, showed positive for polio, sparking the move to introduce the additional ad hoc testing sites. In 2013, the WHO detected the polio virus in 30 sewage samples in Israel, prompting the country — which saw its last case of polio in 1988 — to escalate vaccination efforts.
That’s why Nigeria, which saw its last wild polio case three years ago and hopes to be officially certified as wild polio free in 2020, isn’t resting on its success. If polio is found at any of its sewage testing sites, heath workers canvass the area and immunize all children under the age of 5 within 48 hours. Three to four weeks later, they return to do it again — just to make sure they have covered everyone.
“We cannot in all sincerity say ‘we are polio free’ if we are not actively looking for it,” says Funsho. By sifting through sewage, Funsho and his peers across continents are doing just that — catching the virus before it reaches you.