A Review of Combined Sewer Overflows and Gastrointestinal Illness in a Changing Climate

During a combined sewer overflow (CSO) event, the capacity of a sewer system is exceeded, and untreated sewage, wastewater, and stormwater are released into nearby water bodies. CSOs occur in urban areas due to heavy precipitation, which is expected to occur more frequently and at higher intensity in certain regions of the world due to increasing climate variability. After a CSO, humans can be exposed to pathogens through recreational activities and contaminated drinking water. While previous research has quantified the impacts of CSOs on water quality indicator species and described the effects of CSOs on coastal wetland ecosystems, there is limited research on the potential human health impacts of CSOs. We conducted a literature search of peer-reviewed epidemiological studies that investigated associations between CSOs and human health outcomes. Our literature search and screening methods returned eight studies on the association between CSOs and gastrointestinal (GI) illness in Europe and North America. Our selected peer-reviewed publications included five different study designs: time series, case-crossover, retrospective cohort, case-control, and case time series, with study periods including years 2002 to 2019. The included studies showed evidence of a positive association between CSOs and GI illness, and one study suggested that sewer infrastructure improvements may decrease the burden of GI illness in future decades.

Impact/Purpose

The relationship between heavy rainfall and gastrointestinal (GI) illness has been well-studied in regions with modern wastewater treatment and infrastructure. In Canada, rainfall events greater than the 93rd percentile increased the odds of a waterborne disease outbreak by a factor of 2.283, 95% CI: (1.216, 4.285) based on data from 1975 to 2001 <span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-begin'><span style='mso-spacerun:yes'> ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"a282mmvrn5r","properties":{"formattedCitation":"[1]","plainCitation":"[1]","noteIndex":0},"citationItems":[{"id":96,"uris":["http://zotero.org/users/17589533/items/FGPZGR77"],"itemData":{"id":96,"type":"article-journal","container-title":"International Journal of Environmental Health Research","DOI":"10.1080/09603120600641326","ISSN":"0960-3123, 1369-1619","issue":"3","language":"en","note":"publisher: Informa UK Limited","page":"167-180","source":"Crossref","title":"A role of high impact weather events in waterborne disease outbreaks in Canada, 1975 ¿ 2001","volume":"16","author":[{"family":"Thomas","given":"Kate M."},{"family":"Charron","given":"Dominique F."},{"family":"Waltner-Toews","given":"David"},{"family":"Schuster","given":"Corinne"},{"family":"Maarouf","given":"Abdel R."},{"family":"Holt","given":"John D."}],"issued":{"date-parts":[["2006",6]]}}}],"schema":"https://github.com/citation-style-language/schema/raw/master/csl-citation.json"} [1]<span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-end'>, and a study in the United States (US) found a strong association between disease outbreaks from contaminated surface water and extreme precipitation during the month of the outbreak from 1948 to 1994 <span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-begin'><span style='mso-spacerun:yes'> ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"a295h2imn8m","properties":{"formattedCitation":"[2]","plainCitation":"[2]","noteIndex":0},"citationItems":[{"id":"RmoJ7Jvl/fvlAFUih","uris":["http://zotero.org/users/17589533/items/UK7AWNTN"],"itemData":{"id":2,"type":"article-journal","container-title":"American Journal of Public Health","issue":"8","language":"en","page":"1194¿1199,","title":"The association between extreme precipitation and waterborne disease outbreaks in the United States, 1948-1994","volume":"91","author":[{"family":"Curriero","given":"F.C."},{"family":"Patz","given":"J.A."},{"family":"Rose","given":"J.B."},{"family":"Lele","given":"S."}],"issued":{"date-parts":[["2001",8]]}}}],"schema":"https://github.com/citation-style-language/schema/raw/master/csl-citation.json"} [2]<span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-end'>. In England and Wales, an analysis of waterborne disease outbreaks from 1910 to 1999 showed a significant association between excess cumulative rainfall in the past week and outbreak occurrence <span style='font-size:10.0pt; line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element: field-begin'> ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"a1hf3vfor7n","properties":{"formattedCitation":"[3]","plainCitation":"[3]","noteIndex":0},"citationItems":[{"id":98,"uris":["http://zotero.org/users/17589533/items/D8T59CX7"],"itemData":{"id":98,"type":"article-journal","abstract":"A case-crossover study compared rainfall in the 4 weeks before drinking water related outbreaks with that in the five previous control years. This included public and private drinking water related outbreaks in England and Wales from 1910 to 1999. Of 111 outbreaks, 89 met inclusion criteria and the implicated pathogens included Giardia, Cryptosporidium, E. coli, S. Typhi, S. Paratyphi, Campylobacter and Streptobacillus moniliformis. Weather data was derived from the British Atmospheric Data Centre There was a significant association between excess cumulative rainfall in the previous 7 days and outbreaks (p=0.001). There was an excess of rainfall below 20¿mm for the three weeks previous to this in outbreak compared to control weeks (p=0.002). Cumulative rainfall exceedances were associated with outbreak years. This study provides evidence that both low rainfall and heavy rain precede many drinking water outbreaks and assessing the health impacts of climate change should examine both.","container-title":"Journal of Water and Health","DOI":"10.2166/wh.2009.143","ISSN":"1477-8920, 1996-7829","issue":"1","language":"en","note":"publisher: IWA Publishing","page":"1-8","source":"Crossref","title":"Rainfall and outbreaks of drinking water related disease and in England and Wales","volume":"7","author":[{"family":"Nichols","given":"Gordon"},{"family":"Lane","given":"Chris"},{"family":"Asgari","given":"Nima"},{"family":"Verlander","given":"Neville Q."},{"family":"Charlett","given":"Andre"}],"issued":{"date-parts":[["2009",3,1]]}}}],"schema":"https://github.com/citation-style-language/schema/raw/master/csl-citation.json"} [3]<span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-end'>. However, a review of 24 studies that evaluated an association between extreme precipitation or temperature and waterborne disease, with most study sites located in Asia or North America, reported heterogeneous results across studies, and therefore, recommended further research into effect measure modifiers, such as etiologic agent, geographic region, season, type of water supply, water source, or water treatment <span style='font-size:10.0pt;line-height:150%;font-family:"Times New Roman",serif'><span style='mso-element:field-begin'><span style='mso-spacerun:yes'> ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"a1a9rc905e8","properties":{"formattedCitation&

Citation

Russell, M., B. Haley, E. Slawsky, H. Jardel, K. Cowan, D. Dillon, C. McConaghy, J. Hoffman, AND K. Rappazzo. A Review of Combined Sewer Overflows and Gastrointestinal Illness in a Changing Climate. Springer, Heidelberg, GERMANY, 12:15, (2025). [DOI: 10.1007/s40471-025-00367-5]

DOI: A Review of Combined Sewer Overflows and Gastrointestinal Illness in a Changing Climate