From One Set of Pipes to Another: Gastrointestinal Illness following Sanitary Sewer Overflows.

Sanitary sewer systems collect and carry wastewater from homes, businesses, and industrial sites to treatment facilities. An influx of water during maintenance or rainstorms can overwhelm sewers, sending raw wastewater into the environment in what is known as a sanitary sewer overflow (SSO). SSOs can contaminate drinking water sources, causing gastrointestinal (GI) illness that may be severe enough to send people to the hospital. In a paper published in Environmental Health Perspectives, researchers analyzed data on emergency room (ER) visits for GI illness to determine whether the odds of GI illness increase following an SSO event.1

The researchers used data from four counties in northeastern Massachusetts—Essex, Middlesex, Norfolk, and Suffolk—for the period 2006–2007. During that time, 270 SSOs occurred, and 66,460 people visited ERs for GI illness. For their analysis the authors focused on three “hazard periods” following each SSO: 0–4 d, 5–9 d, and 10–14 d after the event. For both the 0- to 4-d and 5- to 9-d periods the authors found no evidence of an increase in ER visits for GI illness. However, the 10- to 14-d period was associated with an estimated 9% increased odds, on average, of visiting the ER with a GI illness. The strongest association was seen in children between ages 6 and 19 y. These estimates do not account for people with GI illnesses who did not go to the ER, so the overall association might be higher.

An influx of water into sewer lines—often in combination with blockages, line breaks, or other damage—can send raw sewage overflowing into the environment. How can people help prevent SSOs? The two most important ways are not pouring fats or grease down the drain and not flushing sanitary products, even those labeled “flushable.”11 Image: © Dizzy/iStockphoto.

The study “is the first that we know of to quantify an association between SSOs and gastrointestinal illness,” says first author Jyotsna Jagai, an epidemiologist at the University of Illinois at Chicago. Jagai previously estimated that combined sewer overflows in Massachusetts were associated with average increases in GI-related ER visits of 13% for all ages and 32% for elderly people.2 (Combined sewer systems carry both sewage and rainwater, as opposed to sanitary sewer systems, which carry only sewage.)

Up to 75,000 SSOs are estimated to occur annually in the United States.3 Defects in sewer lines, blockages, line breaks, power failures, poor sewer design, and vandalism can all set the stage for overflows, with heavy rainfall a leading cause of the overflows themselves.4 Many sewer systems in the United States are 30–100 years old, making them particularly vulnerable to leaks, blockages, and malfunctions.5,6 Predicted increases in rainfall,6 combined with aging sewer infrastructure, could increase the incidence of GI illnesses related to flooding and sewage spills.

“SSOs pose an upcoming water crisis triggered by deteriorating pipelines and a tendency not to enforce and, in some cases even relax, water quality regulations” says Elena Naumova, chair of the Division of Nutrition Data Sciences at Tufts University’s Friedman School of Nutrition Science and Policy. The price for not paying attention to deteriorating water infrastructure is likely to be decreased productivity and lost lives, predicts Naumova, who was not involved in the new study.

Reporting of SSOs varies with states, and some have no reporting requirements.5 Massachusetts does require SSOs to be reported to the Massachusetts Department of Environmental Protection,7 but the public is not necessarily informed when an overflow occurs. For example, no public notice was issued during a 13-hour discharge of at least 8 million gallons of raw sewage into the Merrimack River in October 2017,8 although residents were later warned to avoid the water. The Merrimack River Watershed Council in Lawrence, Massachusetts, is now advocating for legislation9,10 that would require real-time public notification when raw sewage is discharged into a river or other water body in the state.