On Monday August 15, 2005, the Seneca Lake County Health Department called the manager of the Spraypark to find out whether Spraypark patrons had reported becoming ill. Behind that initial inquiry was State Department of Public Health recognition of the sudden spike in cases of cryptosporidiosis, especially in local day cares in the Seneca Lake area, and the emerging commonality that victims had recently attended the Seneca Lake Spraypark. By that afternoon the Spraypark was closed to the public for the balance of the year.

Over the next week, there was confirmation of a very large outbreak of cryptosporidiosis with the Spraypark as the epicenter. Water samples from the tanks at the Spraypark would reveal a high level of contamination with Cryptosporidium oocysts. The State Department of Health also investigated potential sources of the Cryptosporidium, both human and animal and began a review of the Spraypark’s design and water quality records.

By the end of September, the State Department of Health estimated that approximately 4,000 cases of reported illness were potentially linked to the Spraypark from 37 counties, including 743 confirmed cases.[1] Ultimately, the number of cases the State identified totaled 2,959, including 713 confirmed cases. The graph below depicts the onset dates for both confirmed and suspected cases in the outbreak. What is notable is the duration of the outbreak which includes cases from early July, over a month before the Spraypark was closed. The graph also reflects that cases continued to occur well after the Spraypark was closed. Because infected individuals continue to shed oocysts well after their symptoms end, secondary cases will continue to occur even though the original source of infection has been removed.The New York State Department of Health found that factors contributing to the outbreak included the design of the facility, operator education and awareness, and public awareness and behavior.[2] Given that public behavior is driven by knowledge, or lack of knowledge, of a particular risk, all of these contributing factors were within the control of the State.

An Introduction to Cryptosporidium, A Microscopic Parasite

Cryptosporidium[3] is a protozoan, a single celled parasite. There are many species of Cryptosporidium, but it is now recognized that the most important for human infection is C. hominis.[4] Cryptosporidia are protected by an outer shell that allows them to survive outside the body for long periods of time and makes them very resistant to chlorine-based disinfectants. The disease Cryptosporidium cause is called cryptosporidiosis. Both the parasite and the disease it causes are commonly referred to as “Crypto.” During the past 2 decades, Crypto has become recognized as one of the most common causes of waterborne disease (recreational water and drinking water) in humans in the United States.

The inactive form of Cryptosporidium is called the oocyst. Microscopic but thick-walled, oocysts can survive in a variety of environmental conditions. Once ingested in food or water, Cryptosporidium oocysts multiple rapidly in the intestines triggering the intense diarrhea that characterizes infection with this parasite. As the oocysts replicate and complete their life cycle they are expelled in the bowel movements of infected individuals. A single bowel movement may contain millions of new oocysts. One of the important characteristics of Cryptosporidia oocysts are their extremely small size: 4-6μm[5] or about half the size of a red blood cell.

The life cycle of C. hominis is depicted below and begins with ingestion of the sporulated oocyst, the resistant stage found in the environment. Each oocyst contains 4 infective stages termed sporozoites, which exit from a suture located along one side of the oocyst. The most common site of infection is the last section of the small intestine where sporozoites penetrate individual cells that line the surface where they continue the cycle of division.

Cryptosporidium parvum oocysts in wet mount, under differential interference contrast (DIC) microscopy.  The oocysts are rounded and measure 4.2 µm – 5.4 µm in diameter.  Sporozoites are visible inside the oocysts, indicating that sporulation has occurred.[6]

 Cryptosporidiosis Becomes A Major Problem In The 1980’s

Cryptosporidiosis has long been a veterinary problem, predominantly in young farm animals such as calves. Cryptosporidium was first recognized as a cause of human disease in 1976 but was rarely reported in humans until 1982. The number of detected cases began to rise rapidly along with the AIDS epidemic and the development of methods to identify the parasite in stool samples. The earliest cases of human cryptosporidiosis were diagnosed in animal handlers. An outbreak at a day care center was first documented in 1983.

In 1987, 13,000 people in Carrollton, Georgia, became ill with cryptosporidiosis. This was the first report of its spread through a municipal water system. In the spring of 1993 in Milwaukee, Wisconsin, municipal drinking water was found to be contaminated with Cryptosporidium. An estimated 400,000 people became ill, and the disease contributed to the deaths of numerous immunocompromised persons. These outbreaks focused attention on the risk of waterborne cryptosporidiosis and the need for stricter drinking water standards.

Because of its prominence as an infectious disease, cryptosporidiosis has long been recognized as a public health hazard. As with other well-known diseases, cryptosporidiosis must be reported to public health entities whenever a medical professional or laboratory diagnoses a case.   Cryptosporidiosis was added to the list of reportable diseases in New York State in 1994. By the end 1997 46 states had made cryptosporidiosis a reportable disease.[7] The CDC has long listed it as a nationally notifiable infectious disease.[8]

Cryptosporidiosis Was a Well Known Problem for Recreational Water Features Long Before the Seneca Lake Spraypark Was Built

Since the Milwaukee outbreak in 1993, Crypto has become increasingly associated with recreational water facilities, including pools, water parks, and sprayparks. In a 1999 CDC publication[9] dozens of recreational water outbreaks of Crypto were specifically cited.

The same article, published before ground was even broken on the Seneca Lake Spraypark, offered a variety of defenses against Cryptosporidium:

Prevention plans that combine engineering changes (improved filtration and turnover rates, separate plumbing and filtration for high-risk “kiddie” pools), pool policy modifications (fecal accident response policies, test efficacy of barrier garments such as swim diapers), and patron and staff education should reduce the risk for waterborne disease transmission in public recreational water venues. Education efforts should stress current knowledge about waterborne disease transmission and suggest simple prevention measures such as refraining from pool use during a current or recent diarrheal episode, not swallowing recreational water, using proper diaper changing and handwashing practices, instituting frequent timed bathroom breaks for younger children, and promoting a shower before pool use to remove fecal residue.[10]

As discussed below, none of these basic preventive efforts were followed at Seneca Lake.

In the July/August 2000 issue of Environmental Health, the leading environmental health periodical in the United States, the cover and feature article spotlighted crypto and studies which confirmed the efficacy of UV light in inactivating it.

A 2002 publication noted that 31 outbreaks affecting over 10,000 people had associated cryptosporidiosis with exposure to recreational water.[11] Outbreaks of cryptosporidiosis associated with recreational water facilities continued; indeed, they became more common during the Seneca Lake Spraypark’s years of operations before the outbreak.

The CDC surveillance data for disease outbreaks associate with recreational water for the years 2001-2002 reported that of a total of 65 waterborne disease outbreaks, 30 involved gastroenteritis. And the leading cause of those outbreaks involving gastroenteritis: Cryptosporidium. “Cryptosporidium species remained the most common cause of outbreak associated with treated swimming water (50%)…”[12](emphasis added).

The CDC surveillance data for 2003-2004, identified another 30 outbreaks of gastroenteritis associated with recreational water facilities. Of that number Cryptosporidium was confirmed as the causal agent in 36.7%, and in treated water venues, like the Seneca Lake spray park, Cryptosporidium caused 55.6% (10 or 18) of the gastroenteritis outbreaks.[13] Indeed, Cryptosporidium was identified as the leading cause of outbreaks associated with recreation water in the years 1971 to 2000.[14] Simply put, Cryptosporidium was the number one cause of disease outbreaks in treated recreational water venues for decades prior to the Seneca Lake Crypto outbreak.

Thus, between 2000 and 2005 cryptosporidiosis remained a significant and common public health risk. During that time it was the number one cause of all recreational water illnesses. It had long been on public health radar in the United States, and was widely discussed both in public health circles and within the recreational water industry as a problem that needed to be confronted and dealt with.

Cryptosporidiosis: Symptoms And Person To Person Transmission

Infection with Cryptosporidium results in a wide range of outcomes, from asymptomatic infections to severe, life-threatening illness. The incubation period (time from ingestion to start of symptoms) is an average of 7 days (but can range from 2 to 15 days[15]).  Watery diarrhea is the most frequent symptom of cryptosporidiosis, and can be accompanied by dehydration, weight loss, intense abdominal pain, fever, nausea and vomiting.  In healthy persons, symptoms are usually relatively short lived (1 to 2 weeks), but they can be chronic and far more severe in immunocompromised patients.[16]  While the small intestine is the site most commonly affected, symptomatic Cryptosporidium infections have also been found in other organs including other digestive tract organs, the lungs, and possibly conjunctiva, the clear membrane that covers the eyes.

The most common site of infection is the last section of the small intestine where sporozoites penetrate individual epithelial cells where they continue the cycle of division.

There is currently no drug that can cure cryptosporidiosis. People with competent immune systems will recover on their own and appear to develop some immunity to subsequent infections.

Because of the numbers of oocysts produced by an infected individual and the low infectious dose of Cryptosporidium, person to person or secondary infections are very common during outbreaks. One large study of cryptosporidiosis showed that a significant risk factor is contact with children 4 years and younger due to the increased likelihood of person to person transmission.[17]  The likelihood of secondary infections is large because infected person will continue to shed oocysts weeks after their symptoms resolve.[18] It is also likely that cryptosporidiosis is under recognized and underreported because most physicians will not order the testing needed to identify the parasite even when presented with a symptomatic patient.[19]


[1]           A “confirmed” case is one in which laboratory testing has confirmed the presence of Cryptosporidium oocysts in the victim who must also have an epidemiological link to the source.

[2]           Schaffzin JK, Keithly J, Johnson G, et al. 2006. Large outbreak of cryptosporidiosis associated with a recreational water — New York, 2005 [Abstract]. In: Proceedings of the 55th Annual Conference of the Epidemic Intelligence Service. Atlanta, GA: U.S. Department of Health and Human Services, CDC; 2006.

[3]           Cryptosporidium translates into “hidden spore” (or perhaps more specifically in Latin “underground spore”) reflecting that the spores are indistinguishable or perhaps absent from the oocyst.

[4]           In recent years, other species of Cryptosporidium have been found in humans. C. hominis (formerly C. parvum genotype I), is relatively specific to humans and is morphologically indistinguishable from C. parvum

[5]           A micrometer (also referred to as micron), symbol μm, is one millionth of a meter.

[6]           See, http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Cryptosporidiosis_il.htm.

[7]           Dietz VJ, et. al. National Surveillance for Infection with Cryptosporidium Parvum, 1995-1998: What Have We Learned? PUBLIC HEALTH REPORTS. Vol. 115, 2000.

[8]           See, http://www.cdc.gov/ncphi/disss/nndss/phs/infdis.htm.

[9]           Carpenter C, et. al. Chlorine Disinfection of Recreational Water for Cryptosporidium parvum. EMERGING INFECTIOUS DISEASES. Vol.5, No. 4 July-August 1999.

[10]          Id.

[11]          Dillingham RA ,et. al. Cryptosporidiosis: epidemiology and impact. MICROBES AND INFECT. 4:1059-1066 (2002).

[12]          Yoder JS, et al. Surveillance for Waterborne-Disease Outbreaks Associated with Recreational Water—United States, 2001-2002. MMWR Surveillance Summaries Vol. 53/33-8:1-45; October 22, 2004.

[13]          Dziuban EJ, et al. Surveillance for Waterborne Disease and Outbreaks Associated with Recreatonal Water—United States, 2003-2004. MMWR Surveillance Summaries 55(ss12):1-24; 2006.

[14]          Craun GF, et al., Outbreaks associated with recreational water in the United States. INTERNATL J ENVIRON HEALTH RESEARCH, Vol. 15, Issue 4:243-262; 2005.

[15]          MMWR October 16, 1998 / 47(40);856-860; http://www.cdc.gov/mmwr/preview/mmwrhtml/00055289.htm.

[16]          See CDC Fact Sheet on cryptosporidiosis: http://www.cdc.gov/crypto/disease.html.

[17]          Lake IR, et al., Case-control study of environmental and social factors influencing cryptosporidiosis. EUR J EPIDEMIOL; 22(11): 805–811; 2007.

[18]          Id.

[19]          Morin CA, et al., What do physicians know about cryptosporidiosis? A survey of Connecticut physicians. ARCH INTERN MED;157(9):1017-22; 1997.