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Story Publication logo August 17, 2011

Sewage Science: Anatomy of a Grab Sample



Namdev Koktare is dressed all in white. Spotless white. The white of snowcapped mountains, of Hollywood smiles. It suits him, but it seems a little ill-advised, given what he's about to do.

His job this weekday morning is to collect sewage samples. He's gathering them from canals that serve as garbage dumps and open sewers for two of Mumbai's massive slums.

Koktare shrugs when asked if he's risking ruining his pristine apparel. He's done this task every week for a decade. As he starts to prepare to take the first of the day's grab samples, his fluid motions suggest muscle memory has taken over.

Open SUV rear door. Don surgical mask and medical gloves. Remove paper-wrapped bucket and tray. Grab large glass bottle. Head towards the smell.

India's polio control program samples sewage in three of the country's major urban centers looking for polioviruses. When viruses are found, they are analyzed and compared to earlier findings. The results tell program organizers where the viruses originated. And that tells them where vulnerable children are slipping through the vaccination net. Where efforts need to be stepped up.

Balance kit on wall. Write time, date and location on bottle label. Unwrap bucket and tray, set paper to the side for later. Put bottle in tray. Place funnel lined with muslin in neck of bottle.

Sampling is done in Mumbai, New Delhi and the northeastern city of Patna, not far from the border with Nepal. Patna is the capital of Bihar, one of two highly populated states where polioviruses still haven't been contained by the country's massive vaccination efforts. Migratory workers from Bihar and the other state, Uttar Pradesh, make their way to places like Mumbai for work. They bring their families with them. Polioviruses may come along for the ride. "Sometimes we say that Mumbai is a mixing pot," says Jagadish Deshpande, director of India's Enterovirus Research Center, where the samples will be analyzed.

Koktare is responsible for collecting the Mumbai samples. The method he uses is simple, efficient and about as low tech as you can get. He lowers a metal bucket on a long rope into a canal in which flows what might be called a stream if it weren't choked with garbage and polluted with human effluent. Untreated waste drains into these canals from adjacent shantytowns which are home to hundreds of thousands of India's poor.

Raise bucket hand-over-hand until it clears the wall. Carefully pour gray water through muslin filter. Remove funnel. Stopper bottle.

The grab samples—so named to indicate they are single samples taken at a single point—are timed to catch what scientists involved in environmental surveillance—aka sewage sampling—call morning rush hour. The time when bowels the world over answer nature's call. If polioviruses are in any of the stools that make their way into these canals, they will leach into the water.

Samples need to be collected before the sun gets too high and too hot. Direct sunlight can kill the viruses, Deshpande explains.

Place rope in bucket, add funnel. Strip off latex gloves, place them in bucket or tray. Retrieve paper, wrap it loosely around bucket and tray. Carry kit and bottle back to SUV. Store them carefully in the back.

Koktare goes about the task quickly. He watches the bucket closely when it's in the water, avoiding "solids." The laboratory just wants the sewer water—the eau de toilette, as it were. Solids can complicate test results and aren't needed for the assays done in Deshpande's lab.

Drive to next location.

At each stop it's the same procedure, but a different kit to prevent contaminating one sample with fluid—and potentially viruses—from another location. The first site is a canal that separates Dharavi—once Asia's biggest slum—from a busy highway. Located on what would otherwise be prime property in Mumbai's business district, Dharavi is said to be home to over a million people.

Next is Shivaji Nagar, in the eastern Mumbai suburb of Govandi. There the canal, evident to the nose before the eyes, runs beside a school located a couple of hundred yards from a garbage dump. The third collection site is part of Mumbai's formal sewage system, a pumping station at Wadala in central Mumbai. The spots were selected, Deshpande says, based on years of data pinpointing where paralytic polio cases have been reported in the city. The efforts are focused in the areas with the most reported cases.

Return to the lab.

Once all the samples are collected, Koktare delivers his catch and his kits to technicians at the enterovirus laboratory. (Enteroviruses are RNA viruses like polio that infect via the gastrointestinal tract.) Equipment heads to the autoclave, a machine that sterilizes reusable items by subjecting them to high pressure, high temperature steam. The bottles are put in the fridge overnight so the tiny particles of whatever the water invariably contains have a chance to settle out. The liquid is later centrifuged and concentrated, then tested for polioviruses.

With India seemingly on the verge of stopping polio transmission, samples aren't yielding wild polioviruses these days. Scientists use the term "wild" to distinguish natural viruses from the genetically modified ones contained in the live virus polio vaccine used by India and many other countries. Vaccine viruses, which are found all the time, are of interest, but right now they're more of an incidental catch when it comes to India's sewage sampling endeavors. At this point, Deshpande's lab hasn't found a wild poliovirus since last November—an interval that would have been unimaginable only a few years ago.



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