Giardia outbreak in the Mohawk Watershed
Thirty-two students at Union College diagnosed
An outbreak of Giardia has been identified on the Union College Campus in Schenectady NY. This outbreak occurs while faculty, students, and staff are carefully monitoring personal health during the Covid-19 pandemic. Little is known as to the source of the infection, but it is possible that local impaired streams may be the vector. Curiously, a water main break in Schenectady in late September caused a local disruption of municipal water. This post explores the outbreak and possible sources.
The outbreak at Union involves 32 students and was first reported on 23 October 2020 by Dan Wilcox in the Concordiensis, the College newspaper [1], It was then reported by the Daily Gazette on 25 October 2020 [2]. The Concordiensis article provides a rough timeline on infections: 18 students were infected by 16 October, and 32 were infected by 23 October. Given the typical incubation period of 7-14 days, this may mean that exposure occurred in early October or late September. Some students report the onset of symptoms as early as early October, but it is unclear whether exposures occurred in a short time window or over an extended period. The source of the outbreak remains unknown.
Dan Wilcox explains that communication from the College indicate that some students had entered bodies of water that are “not designated” as swimming areas, specifically the Hans Groot Kill (an impaired urban stream that traverses campus and empties into the Mohawk River), and the Plotterkill, a rural stream in western Schenectady County that is a short drive from campus [1]. Other than the general timeline and the possible contact with local streams, there is not enough information in the articles to determine whether the cases have a common origin or the specific timing of infections.
Warning signs along the Hans Groot Kill on the Union College Campus. These new signs hint that impaired water may be harmful if contacted. These signs resulted from the October 2020 Giardia outbreak. Photo: Eva Willard-Bauer, 27 October 2020.
Giardia
It is estimated that there are 200-375 million diarrheal illnesses annually in the US, and the majority of cases (~90%) are caused by viral (i.e., rotovirus, norovirus) and bacterial (e.g., Salmonella spp, Shigella spp, Escherichia coli) pathogens. A much smaller percentage of cases are caused by intestinal protozoan parasites, which include Cryptosporidium and Giardia [5]. Giardia lamblia (synonymous with G. intestinalis or G. duodenalis, herein “Giardia”) result in over 1 m infections per year in the US [5, 9, 24]. Giardia is a National Notifiable Disease and is tracked by the CDC through its National Notifiable Diseases Surveillance System (NNDSS) that tracks ~120 diseases [6,11].
The hallmark of Giardia is diarrhea, but it can be accompanied by a number of gastrointestinal symptoms including flatulence, bloating, weight loss, abdominal cramping, nausea, malabsorption, and others [7]. Cysts can be excreted for weeks or months [7].
According to the CDC, Giardia has a high occurrence in the Northeast (~27% cases). Incidences in the State are 8.4 (per 100,000) and 13.3 (per 100,000) in NYC, which is the highest reported large population center in the country [5]. It is certain that the reported cases are lower than actual cases and there are likely somewhere between 0.1 to 2.5 million annual infections in the United States [7].
Giardia is spread from people or animals to people from fecal to oral transmission and has an incubation period with a median of 7-10 days, but the overall range is between 3 and 25 days [7]. Voluntary humans and “voluntary” beavers were purposely infected with Giardia cysts, and the onset of symptoms was between 10 and 14 days for beavers and between 6 and 17 days in humans [10].
Infection occurs through the transmission of cysts though person-to-person contact, or through contaminated food or water. There is an annual seasonality to reported cases, which are highest in the late summer and early fall, so the CDC sees many reported cases in September and October. Waterborne outbreaks are related to contaminated drinking water, or contact with contaminated recreational water such as stream, rivers, and lakes [7].
Fecal-oral transmission is the primary route of Giardia infection. It is that simple. Transmission can occur through direct or indirect contact with human waste, contaminated food (poor handling), or contaminated water are common sources. Person-to-person transmission is not uncommon in those involved with childcare and contact with other similarly ill people [24].
The low infectious dose (as low as 10 cysts) makes contact tracing difficult, and is another reason that contact with drinking water and recreational water relatively common [9,11]. Giardia transmission in drinking water has been identified as the single most common cause of drinking water outbreaks reported in the US and it may account for nearly 1/3 of all cases with known etiology [11]. Zoonotic transmission is thought to be of minor importance in North America, but it is clear from a number of case studies that a source of Giardia can be aquatic mammals (i.e. beavers, muskrats) in drinking water sources [9].
Outbreaks
Giardia infections are either sporadic (single, isolated cases sometimes called “non-outbreak”), or in an outbreak (multiple cases) where a cluster of cases exceeds what is normally expected [4, 5, 23, 24]. The vast majority of cases in the US are sporadic, with outbreak cases only accounting for 1-2% of annual cases [23]. Thus the Union College outbreak in Schenectady NY is an unusual occurrence. Most outbreaks appear to be related to contaminated drinking water and therefore prevention is directed to remediating failures in drinking water systems. For sporadic (non-outbreak) Giardia infections, prevention is different: it is focused on risk reduction associated with handling diapers, sexual contact, swimming in untreated water, and drinking untreated or impaired water [17].
In typical outbreaks, diagnosed cases tend to provide a minimum estimate of total numbers infected (see examples below), but strict health surveillance on campus due to Covid-19 means that students are extra cautious about daily reporting symptoms out of the ordinary. Thus this may be a unique outbreak where a large fraction of total infected people are known. The obvious exception would be those students who have Giardia, but are asymptomatic. The number of asymptomatic cases may be between 10 and 20% [3].
In a typical outbreak, there are three likely possible sources of the Giardia cysts that cause infection: 1) contaminated streams/lakes; 2) contaminated drinking water; and 3) contaminated food. By far the most common for outbreaks is a contaminated drinking water supply, and foodborne outbreaks are uncommon [11].
Between 2011 and 2016 worldwide reported (and documented) occurrences of waterborne outbreaks of protozoan parasites are summarized in Efstratiou and colleagues [4]. Of these outbreaks, many of which were in the US (41%), the etiological agent was Cryptosporidium in 63% of the cases and Giardia in 37% of the cases. Of all cases, 82% appear to be related to contaminated drinking water supplies, and 14% were related to impaired recreational water, and almost all of these are cases of Cryptosporidium (many from treated recreational water in swimming pools). Thus almost all of the outbreaks of Giardia were related to impaired drinking water, which includes untreated water, contaminated sources, failure in treatment, or post-treatment contamination.
Regional outbreaks
An outbreak in Rome NY in 1974-75 was linked to Giardia in the municipal water supply. Some 350 people had confirmed cases, but the total number affected was likely to be as high as 5300 people (including asymptomatic cases) [9]. At the time this was the largest outbreak in the US. The infection rate has been estimated to have been >10% and those affected reported drinking more than one glass of untreated municipal water a day. The first cases likely occurred in November and cases continued to June 1975, but a significant numbers of cases lasted for six months (Dec to May) [13].
Epidemiological investigations in the Rome NY case showed that the only commonality among the majority of cases was consumption of municipal water, and thus this was suspected as the source. The municipal water supply was in the Fish Creek watershed, and chlorination was used, but not filtration, before water was distributed to the municipality. Giardia cysts were eventually found in an exhaustive search in source reservoir to the municipal water, and experiments with pathogen-free Beagle puppies produced human G. lamblia after the puppies were given large quantities of municipal water [13].
The Rome NY outbreak occurred in a time where the effect of chlorination in Giardia was incompletely known. Peter Shaw and colleagues concluded: “Chlorination procedures in Rome were clearly inadequate to prevent waterborne transmission of giardiasis.” but they also noted that “...chlorination may not be a reliable method for eradicating viable giardia cysts from water” because municipal chlorination is of insufficient strength to kill Giardia cysts.” [13].
A 1985-86 outbreak in Pittsfield Massachusetts resulted in at least 703 cases of people infected from municipal water after an auxiliary reservoir was temporarily used for the town’s water supply [8]. Two weeks after switching to the alternate reservoir, diagnosed cases started to appear, and the water source was changed back to the original two reservoirs, but the outbreak continued for three months [6].
In the Pittsfield case, the municipal drinking water was not filtered, and there seems to have been a malfunction of the chlorination system during the initial use of an auxiliary reservoir so that there were only low levels of chlorine in that supply for a time during the source switch [12]. Nearly three quarters of people infected reported drinking two or more classes of municipal water per day [8]. Later studies showed that beavers and muskrats likely facilitated spread of Giardia in the auxiliary reservoir, but it is suspect that that they were originally infected by humans because of the sub-type of Giardia present [“A” type – see 12].
The more recent regional case occurred in September 2009, when 36 cases of Giardia were traced to a roadside spring on Route 22 in Stephentown in eastern Rensselaer County (NY). People infected were from Albany, Rensselaer, Schenectady, and Suffolk counties in NY, and from Massachusetts. The spring was destroyed after Giardia cysts were found in the water [8].
Some important lessons emerge from these and other recent outbreaks in the US: 1) outbreaks are not common; 2) almost all outbreaks are related to drinking water supply; 3) detection of Giardia in municipal water is very difficult; 4) the results of bacteria tests (i.e. Coliform bacteria, E. coli, etc.) are not reliable indicators for the presence or absence of Giardia in water [14; 20]; and 5) the moderate tolerance of Giardia to chlorination means that it can be present in chlorinated municipal water.
Chlorination of municipal water
Chlorination has long been the first line defense that municipalities have in eliminating or reducing pathogens in water supplies. I recently wrote about early attempts to stop the cholera epidemic of 1832 by using chloride of lime in local wells in Schenectady NY [16]. It is now appreciated that Giardia has a moderate tolerance of chlorine, and therefore can survive in some chlorinated systems [11,20].
The organism can also exploit systems with partly impaired chlorination systems as in the Pittsfield outbreak in 1984-85. It is also worth bearing in mind that a well-recognized source of Giardia and Cryptosporidium is chlorinated swimming pools used by infants and young children [7]. This is especially important for the Cryptosporidium parasite that is extremely resistant to chlorination, and is therefore commonly associated with outbreaks associated with typical chlorinated drinking water and swimming pools [4].
We can conclude from the literature that chlorine disinfection of surface water sources of drinking water is insufficient and pre-treatment with sedimentation and then filtration is required [14,20]. A key point is that water quality data from Giardia outbreaks show that negative tests for bacteria in drinking water (such as coliform bacteria) are not reliable indicators whether the water is potentially contaminated with Giardia [14].
Local suspects
Recall that with any outbreak of Giardia, the prime suspect is contaminated water. Most cases involve drinking water contamination, but contact with local streams and rivers are also a possibility.
The small, impaired urban stream that flows through the Union Campus is the Hans Groot Kill, and it has been implicated in this outbreak because some students report contact with stream water [1]. Our research group has been studying pathogens in the Hand Groot Kill for several years, and a primary tool we have been using is measurement of fecal indicator bacteria (FIB). Much of this work is the thesis effort of Eva Willard-Brauer, a geology-environmental science double major at Union. We have been testing for Enterococci sp., but also E. coli, both fecal indicator bacteria [22].
The stream is highly contaminated. Our results, which we published last March 2020 for the Mohawk Watershed Symposium, show that pathogen levels in this stream are so high that it is almost certain that raw sewage is entering the stream at high flow, low flow, winter and summer [22]. In this paper we wrote:
“...it is likely that the stormwater [in the Hans Groot Kill] is contaminated by sewage from leaking and/or illegally-connected sanitary sewer mains. These findings highlight the role of infrastructure failures – both in design and maintenance – as a pollution source in the Mohawk Watershed.”
“The [Hans Groot Kill] HGK presents a health hazard to the public, particularly given its presence on a college campus and a residential neighborhood. For the time being, signage should be placed amongst the frequented areas of the stream where people may wade or where children may play. This simple action may help to limit the number of people that could be adversely affected by exposure to Enterococci and other FIB in the HGK... It would surely be in the best interest of the City of Schenectady and New York State to repair the pipes that are currently delivering bacteria-laden sewage to the HGK and the Mohawk River.” [22]
In most Giardia outbreaks a key concern is the integrity of the drinking water supply. Schenectady gets its water from a wellfield on the floodplain of the Mohawk River, and the system was stressed this summer due to low water and drought conditions (see a post about that issue here). But water levels on the Mohawk have been low, and the wellfield has not flooded this year, so contamination at the source seems unlikely. In some Giardia outbreaks it is not the water source, but rather the distribution system that allows contaminated water into the system. In this situation the water is still chlorinated, so typical tests for bacteria would be negative even though the water may have parasites provided they can tolerate chlorine levels typical in municipal waters (i.e., Cryptosporidium or Giardia). When distribution systems are compromised it is not uncommon for Boil Water Advisories (BWA) to be issued, and the most common reason for a BWA is a broken water main [25].
As fate would have it, there was a major water main break in Schenectady on 18 September 2020. The Daily Gazette reported the water main break in a primary distribution system occurred near the Craig Street bridge between 18-19 September [18,19]. The break occurred in a 36-inch water main that resulted in closure of I-890 between Broadway and Michigan Avenue. A boil water advisory (BWA) was not issued but the City urged residents who experienced discoloration to flush their water for 4-5 minutes [19]. Some residents reported sediment and purple-grayish sludge in their water [21]. This was not a minor leak: the mayor estimated the amount of water spilled on the order of millions of gallons. According to the press, the cause of the pipe break was unknown, but there is a suggestion that it was related to hillside erosion [19]
Is it possible that this break in the distribution system locally compromised the city water supply? The timing of this water main break would allow for early reported Giardia cases. Recall that in the Pittsfield outbreak, cases were reported two weeks after impairment. If this is a similar situation, we would predict first cases by about 28 Sept to 1 Oct. This possibility would explain why some infected students reported that they did not have any contact with local creeks or streams. In this scenario, it is possible that consumption of large quantities of untreated municipal water may be a common link between cases (as opposed to swimming in impaired water). The implications for the epidemiology in these two contrasting scenarios could not be more different.
In the latter scenario, why would just Union students be infected? There are several things to consider. One is that perhaps cases are more widespread, but they remain unreported, a situation common to almost all outbreaks [24]. Let’s face it: people tend to be reluctant to talk about diarrhea, especially their own. However, another reason may be related to the unique situation on Campus related to Covid-19. The intense daily self-reporting of personal health required of Union students due to Covid-19 restrictions may have resulted in this outbreak being extremely well-recognized on campus, but not elsewhere. It would seem prudent that residents in Schenectady who experienced symptoms (diarrhea) in the last month to report this to the Schenectady County Public Health Department (here).
We may never have a definitive conclusion as to the source of this outbreak, but it seems wise to act swiftly now to capture data from individuals who have been infected. This task certainly may be complicated during monitoring and surveillance associated with Covid-19, but determination as to whether this outbreak has a wider extent may be especially important for immunosuppressed individuals [20].
Whether the source of the outbreak is a contaminated stream or municipal water, both scenarios have a common thread: our water infrastructure needs attention and investment. Broken and leaky pipes have the potential to adversely affect human health.
This and other Notes from a Watershed are available at: https://mohawk.substack.com/
Further Reading
[1] Wilcox, Dan, 23 October 2020, “Cases of Giardiasis rise to at least 32” Concordiensis (Union College, Schenectady NY).
[2] Mason, Zach, 25 October 2020, “32 Union College students sickened by intestinal disease Giardiasis” Daily Gazette (Schenectady NY).
[3] Wolfe, M.S., 1992. Giardiasis. Clinical microbiology reviews, 5(1), pp.93-100.
[4] Efstratiou, A., Ongerth, J.E. and Karanis, P., 2017. Waterborne transmission of protozoan parasites: review of worldwide outbreaks-an update 2011–2016. Water research, 114, pp.14-22.
[5] Centers for Disease Control and Prevention (CDC). 2019. Giardiasis Summary Report —National Notifiable Diseases Surveillance System, United States, 2018. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC (Link).
[6] CDC National Notifiable Diseases Surveillance System (NNDSS) (Link)
[7] Furness, BW, Beach, MJ, and Roberts, JM, 2000. Giardiasis Surveillance --- United States, 1992—1997 (Link)
[8] Bedard, B., Elder, R., Phillips, L, and Wachunas, M. (2016). Giardia outbreak associated with a roadside spring in Rensselaer County, New York. Epidemiology and Infection, 144(14), 3013-3016. doi:10.1017/S0950268816001497
[9] Bartelt, L.A., Attias, E. and Black, J., 2016. Epidemiology of cryptosporidiosis and giardiasis: What pediatricians need to know. Current Tropical Medicine Reports, 3(3), pp.108-114.
[10] Prasad, B., Ryan, M.O. and Haas, C.N., 2017. A method for incorporating a time-dose-response model into a Giardia lamblia outbreak. Journal of Water and Health, 15(4), pp.490-504.
[11] Yoder, J. S., Gargano, J. W., Wallace, R. M. & Beach, M. J., 2012, Giardiasis surveillance–United States, 2009–2010. Morbidity and Mortality Weekly Report: Surveillance Summaries 61 (5), 13–23.
[12] Kent, G. P., Greenspan, J. R., Herndon, J. L., Mofenson, L. M.,Harris, J., Eng, T. R. & Waskin, H. A. 1988. Epidemic giardiasis caused by a contaminated public water supply. American Journal of Public Health 78 (2), 139–143.
[13] Shaw, P.K., Brodsky, R.E., Lyman, D.O., Wood, B.T., Hibler, C.P., Healy, G.R., MacLeod, K.I., Stahl, W. and Schultz, M.G., 1977. A community wide outbreak of giardiasis with evidence of transmission by a municipal water supply. Annals of Internal Medicine, 87(4), pp.426-432.
[14] Craun, G.F., 1979. Waterborne giardiasis in the United States: a review. American journal of public health, 69(8), pp.817-819.
[15] Lin, S.D., 1985. Giardia lamblia and water supply. Journal‐American Water Works Association, 77(2), pp.40-47.
[16] Garver, J.I., 2019. The 1832 Cholera epidemic on the Mohawk -https://mohawk.substack.com/p/1832-cholera-epidemic-on-the-mohawk
[17] Reses HE, Gargano JW, Liang JL, Cronquist A, Smith K, Collier SA, Roy SL, Vanden Eng J, Bogard A, Lee B, Hlavsa MC, Rosenberg ES, Fullerton KE, Beach MJ, Yoder JS. Risk factors for sporadic Giardia infection in the USA: a case-control study in Colorado and Minnesota. Epidemiol Infect. 2018 Jul;146(9):1071-1078. doi: 10.1017/S0950268818001073. Epub 2018 May 9. PMID: 29739483.
[18] Staff reporter, 20 Sept 2020. Water main break shuts down part of I-890, Daily Gazette (Schenectady, NY). (Link)
[19] DeMola, Peter, 21 Sept 2020. Repairs underway for broken water main in Schenectady, Daily Gazette (Schenectady, NY). (Link)
[20] Sexton, L.M., 1994. A survey of source and finished water supplies for Giardia cysts and cryptosporidium oocysts. MSc Thesis, University of Kentucky, Kentucky Water Resources Institute. 100 p.
[21] Jack Summers, Jack. 20 Sept 2020.“Water main break in Schenectady fixed, road reopened, no boil water advisory issued” News10. (Link)
[22] Willard-Bauer, E., Smith, J.A, Garver, J.I., Goldman, D., Newcomer, B., 2020. Enterococci levels in the Hans Groot Kill and Mohawk River, Schenectady, NY. In Garver, J.I., Smith, J.A., and Rodak, C. 2020. Proceedings of the 2020 Mohawk Watershed Symposium, Union College, Schenectady, NY, March 20, 2020, Volume 12, p. 63-68. (Link to paper here).
[23] Daly, E.R., Roy, S.J., Blaney, D.D., Manning, J.S., Hill, V.R., Xiao, L. and Stull, J.W., 2010. Outbreak of giardiasis associated with a community drinking-water source. Epidemiology & Infection, 138(4), pp.491-500.
[24] Benedict KM, Collier SA, Marder EP, Hlavsa MC, Fullerton KE, Yoder JS (2019). Case–case analyses of cryptosporidiosis and giardiasis using routine national surveillance data in the United States – 2005–2015. Epidemiology and Infection 147, e178, 1–5. (Link)
[25] Vedachalam, S., John, M.E. and Riha, S.J., 2014. Spatial analysis of boil water advisories issued during an extreme weather event in the Hudson River Watershed, USA. Applied Geography, 48, pp.112-121.