At a glance
Background
Cryptosporidiosis is a gastrointestinal illness caused by protozoa of the genus Cryptosporidium, a leading cause of U.S. waterborne disease outbreaks (1) and U.S. zoonotic enteric illness (2,3). An estimated 823,000 cryptosporidiosis cases occur annually; this means <2% of cases are nationally notified (4). Cryptosporidium infection can be symptomatic or asymptomatic. Immunocompetent patients can experience frequent, non-bloody, watery diarrhea typically lasting one to two weeks. Additional symptoms can include vomiting, nausea, abdominal pain, fever, anorexia, fatigue, and weight loss. Immunocompromised patients can experience profuse watery diarrhea lasting weeks to months or even life-threatening malnutrition and wasting (5).
Cryptosporidiosis is a nationally notifiable disease; the first full year of reporting was 1995. National data are collected through passive surveillance. Healthcare providers and laboratories that diagnose cryptosporidiosis are mandated to report cases to the local, state, or territorial health department. The 50 states, District of Columbia (DC), New York City (NYC), and territorial public health agencies, in turn, voluntarily notify CDC of cases via the National Notifiable Disease Surveillance System (NNDSS). Although tribes do not report directly to CDC via NNDSS, the inclusion of case data submitted by states for American Indian and Alaskan Native individuals residing on tribal lands may vary based on laboratory and case reporting practices in each jurisdiction, the location where healthcare services were delivered, and other relevant factors. Some jurisdictions conduct enhanced molecular surveillance of cryptosporidiosis through participation in CryptoNet; CryptoNet data are not presented here.
State, territorial, local, and tribal health agencies voluntarily notify CDC of cryptosporidiosis outbreaks via the National Outbreak Reporting System (NORS). NORS data are not presented here; however, summaries of data on waterborne disease outbreaks are reported elsewhere.
Methods
Case definition
The definition of a confirmed case of cryptosporidiosis has changed over time. The first national case definition was published in 1995 (6); the current case definition was published in 2012 (7). The pre-2011 case definitions classified a case with any laboratory evidence of Cryptosporidium infection as a confirmed case.
The 2012 confirmed case definition requires evidence of Cryptosporidium organisms or DNA in stool, intestinal fluid, tissue samples, biopsy specimens, or other biological sample by certain laboratory methods with a high positive predictive value (e.g., direct fluorescent antibody [DFA] test, polymerase chain reaction [PCR], enzyme immunoassay [EIA], or light microscopy of stained specimen).
A probable case of cryptosporidiosis is defined as 1) having supportive laboratory test results for Cryptosporidium spp. infection using a screening test method, such as immunochromatographic card or rapid card test, or a laboratory test of unknown method or 2) meeting clinical criteria (diarrhea and one or more of the following: diarrhea duration of >72 hours, abdominal cramping, vomiting, or anorexia) and being epidemiologically linked to a confirmed case.
A suspect case is defined as having a diarrheal illness and being epidemiologically linked to a probable case. Cases not classified as confirmed, probable, or suspect are classified as unknown.
Analysis
National cryptosporidiosis surveillance data for 2020 were analyzed using R version 4.4.1. Data cleaning processes included case deduplication and the verification of case status (confirmed or non-confirmed). Numbers, percentages, and incidence rates (cases per 100,000 population) of cryptosporidiosis were calculated in aggregate for the United States and separately for each reporting jurisdiction. Rates were calculated by dividing the number of cryptosporidiosis cases by each year's mid-year census estimates (8,9) and multiplying by 100,000.
U.S. Census Bureau data were obtained using its Application Programming Interface and the R "tidycensus" package (10,11). Region and total population estimates included only jurisdictions that reported (Figure 2). In addition to analyzing data nationally and by reporting jurisdiction, data were analyzed by region (Northeast, Midwest, South, West, and Territories), as defined by the U.S. Census Bureau (12). To account for differences in the seasonal use of recreational water, the West region was further subdivided into Northwest and Southwest.
To examine reporting over time, cryptosporidiosis rates were calculated by year (2011 to 2020). To examine changes in cryptosporidiosis reporting in 2020 attributed to the COVID-19 pandemic, we calculated the percent change in incidence between 2019 and 2020. We also calculated the five-year average-annual incidence (2016-2020). Annual cryptosporidiosis rates were calculated by demographic variables (age and sex) and jurisdiction. Rates were not calculated for race or ethnicity due to large proportions of missing data for these variables (16.1% and 25.8%, respectively).
Findings
In 2020, 53 jurisdictions reported cryptosporidiosis case data to NNDSS, including 50 states, 1 territory, DC, and New York City. There were 7,622 cases of cryptosporidiosis reported to CDC with an average annual incidence of 2.3 cases per 100,000 population (Figure 1, Table 1). Reported cases of cryptosporidiosis in 2020 were lower than those reported in previous years, with a 46.5% decrease in incidence from 2019 (incidence of 4.3 cases per 100,000) (Table 1). This lower rate may be attributed, in part, to the COVID-19 pandemic, when healthcare providers and local, state, and territorial health departments in the United States may have had lower capacity to detect, investigate, and report cases. A decrease in incidence was observed across all but three reporting jurisdictions (Table 1), with the percent decrease in incidence ranging from 14.6% to 75.0%. Of the 7,622 reported cases in 2020, 5,834 (76.5%) were confirmed, while 1,788 cases (23.5%) were not confirmed. This is a slight increase in the proportion of confirmed cases compared with 2019 (72.9%), though the proportion of confirmed cases has increased slightly over time, with 65.8% confirmed in 2011. There were 74 outbreak-associated cases in 2020.
Cryptosporidiosis is geographically widespread across the United States. By region, incidence of reported cryptosporidiosis cases ranged from 1.3 cases per 100,000 population in the Southwest to 4.0 cases per 100,000 population in the Midwest. In 2020, the U.S. territory of Puerto Rico had an annual incidence of 0.1 per 100,000. By jurisdiction, cryptosporidiosis incidence ranged from 0.1 per 100,000 population in Puerto Rico to 11.6 per 100,000 population in Iowa (Table 1, Figure 2). Differences in incidence might reflect differences in risk factors or mode of transmission of cryptosporidium; the magnitude of outbreaks; or the capacity or requirements to detect, investigate, and report cases.
For cases with a reported symptom onset date, most cases occurred between July and August, with a peak in July (n=693). There was also a peak in reported cases in January (n=650) (Figure 3). When separated by region, the Northeast and Midwest had the most distinct pattern of July and August peaks (Figure 4). In contrast, the South and Southwest regions had a distinctly higher number of cases in January, with the South reporting a more consistent number of cases during the remainder of the year (Figure 4).
During 2020, a total of 3,733 cases were male (49.0%) and 3,838 (50.4%) were female (Table 2). most cases for which data on race were available occurred among the classifications White (69.1%), Black (7.4%), other or Multi-race (5.7%), and Asian/Pacific Islander (1.1%). Most patients for whom data on ethnicity were available were non-Hispanic (66.7%). Data on race were not included for 16.1% of total annual cases, and data on ethnicity were not reported for 25.8% of case reports.
With respect to age, the incidence of reported cryptosporidiosis cases was highest among cases in persons aged <5 years and 20-34 years (incidence rates = 4.1 and 3.0-3.3 cases per 100,000 population, respectively) (Figure 5). Broken down by sex, the highest incidence of cryptosporidiosis was among boys aged <5 years (4.3 cases per 100,000 population). Rates were similar between male and female patients for every age group, with the greatest difference in incidence being 0.7 cases per 100,000 for the <5 years age category. (Figure 6)
Acknowledgements
This report is based on contributions by state and local epidemiologists and microbiologists. The authors gratefully acknowledge Zainab Salah for assistance in reviewing code, and thank Catherine Hough, Samaria Aluko-Estrella, Amanda MacGurn, Vincent Hill, and Jeremy Sobel for their assistance in publishing this annual report.
Tables and figures
*Cases per 100,000 population
§ In total, 70,464 cases were confirmed (67.8%); 33,420 cases were non-confirmed (32.2%). For 2020, 5,834 cases were confirmed (76.5%); 1,788 cases were non-confirmed (23.5%).
| Region/Jurisdiction | No. | % | Incidence | Five-Year Avg. Incidence | Incidence Year Prior | Percent Change | No. of outbreak- associated cases |
|---|---|---|---|---|---|---|---|
| Northeast | 1256 | 16.5 | 2.2 | 3 | 4 | -45 | 21 |
| Connecticut | 33 | 0.4 | 0.9 | 1.8 | 2.2 | -59.1 | |
| Maine | 72 | 0.9 | 5.3 | 4.6 | 5.3 | 0 | 7 |
| Massachusetts | 120 | 1.6 | 1.7 | 2.7 | 3.4 | -50 | |
| New Hampshire | 40 | 0.5 | 2.9 | 4.7 | 4.8 | -39.6 | |
| New Jersey | 118 | 1.5 | 1.3 | 2 | 3.2 | -59.4 | |
| New York City¶ | 105 | 1.4 | 1.2 | 2.6 | 4.8 | -75 | 12 |
| New York State¶ | 390 | 5.1 | 3.7 | 3.3 | 4.4 | -15.9 | |
| Pennsylvania | 299 | 3.9 | 2.3 | 3.4 | 4 | -42.5 | 2 |
| Rhode Island | 23 | 0.3 | 2.2 | 4.3 | 6 | -63.3 | |
| Vermont | 56 | 0.7 | 9 | 8.7 | 4.6 | 95.7 | |
| Midwest | 2712 | 35.6 | 4 | 6.5 | 6.6 | -39.4 | 13 |
| Illinois | 242 | 3.2 | 1.9 | 2.7 | 3.2 | -40.6 | |
| Indiana | 160 | 2.1 | 2.4 | 3.7 | 4.8 | -50 | |
| Iowa | 368 | 4.8 | 11.6 | 18.3 | 17.7 | -34.5 | |
| Kansas | 79 | 1 | 2.7 | 4 | 4.8 | -43.7 | |
| Michigan | 246 | 3.2 | 2.5 | 3.8 | 4.2 | -40.5 | |
| Minnesota | 369 | 4.8 | 6.5 | 8.3 | 8.6 | -24.4 | 1 |
| Missouri | 228 | 3 | 3.7 | 5.6 | 6.5 | -43.1 | |
| Nebraska | 107 | 1.4 | 5.5 | 9.7 | 10 | -45 | 9 |
| North Dakota | 24 | 0.3 | 3.1 | 4.7 | 5 | -38 | 2 |
| Ohio | 326 | 4.3 | 2.8 | 7.3 | 5.9 | -52.5 | 1 |
| South Dakota | 76 | 1 | 8.5 | 16.9 | 18.8 | -54.8 | |
| Wisconsin | 487 | 6.4 | 8.3 | 12.6 | 12.5 | -33.6 | |
| South | 2445 | 32.1 | 1.9 | 3 | 4 | -52.5 | 16 |
| Alabama | 137 | 1.8 | 2.8 | 4.3 | 4.6 | -39.1 | |
| Arkansas | 66 | 0.9 | 2.2 | 3.3 | 4.7 | -53.2 | |
| Delaware | 25 | 0.3 | 2.5 | 3.2 | 4 | -37.5 | |
| District of Columbia | 12 | 0.2 | 1.7 | 4.1 | 4.4 | -61.4 | |
| Florida | 291 | 3.8 | 1.3 | 2.5 | 3.1 | -58.1 | 5 |
| Georgia | 250 | 3.3 | 2.3 | 3.2 | 3.4 | -32.4 | |
| Kentucky | 222 | 2.9 | 5 | 4.3 | 7.6 | -34.2 | |
| Louisiana | 106 | 1.4 | 2.3 | 3.8 | 7.6 | -69.7 | |
| Maryland | 72 | 0.9 | 1.2 | 1.6 | 1.8 | -33.3 | |
| Mississippi | 64 | 0.8 | 2.2 | 2.7 | 4.2 | -47.6 | |
| North Carolina | 205 | 2.7 | 1.9 | 2.4 | 2.7 | -29.6 | |
| Oklahoma | 102 | 1.3 | 2.6 | 4.5 | 4.9 | -46.9 | |
| South Carolina | 85 | 1.1 | 1.6 | 2.1 | 2.2 | -27.3 | |
| Tennessee | 183 | 2.4 | 2.7 | 3.1 | 3.6 | -25 | 1 |
| Texas | 365 | 4.8 | 1.2 | 3.1 | 4.1 | -70.7 | 3 |
| Virginia | 198 | 2.6 | 2.3 | 3.6 | 6.1 | -62.3 | 4 |
| West Virginia | 62 | 0.8 | 3.5 | 3.4 | 4.1 | -14.6 | 3 |
| Northwest | 421 | 5.5 | 2.6 | 4.1 | 4.5 | -42.2 | 15 |
| Alaska | 6 | 0.1 | 0.8 | 1.7 | 1.6 | -50 | |
| Idaho | 88 | 1.2 | 4.8 | 6.5 | 7.3 | -34.2 | 3 |
| Montana | 48 | 0.6 | 4.4 | 6.2 | 6.7 | -34.3 | |
| Oregon | 95 | 1.2 | 2.2 | 6.1 | 6 | -63.3 | |
| Washington | 172 | 2.3 | 2.2 | 2.3 | 3 | -26.7 | 12 |
| Wyoming | 12 | 0.2 | 2.1 | 3.3 | 3.8 | -44.7 | |
| Southwest | 785 | 10.3 | 1.3 | 2.1 | 2.4 | -45.8 | 9 |
| Arizona | 80 | 1 | 1.1 | 3.1 | 2 | -45 | 4 |
| California | 367 | 4.8 | 0.9 | 1.4 | 1.8 | -50 | |
| Colorado | 149 | 2 | 2.6 | 3.7 | 4.7 | -44.7 | 3 |
| Hawaii | 4 | 0.1 | 0.3 | 0.5 | 0.6 | -50 | |
| Nevada | 21 | 0.3 | 0.7 | 1.1 | 1.6 | -56.2 | |
| New Mexico | 36 | 0.5 | 1.7 | 3.9 | 4 | -57.5 | |
| Utah | 128 | 1.7 | 3.9 | 5.1 | 6.1 | -36.1 | 2 |
| Territories | 3 | 0 | 0.1 | 0 | 0 | 0 | 0 |
| Puerto Rico | 3 | 0 | 0.1 | 0 | 0.1 | -100 | |
| Guam | |||||||
| Northern Mariana Islands | |||||||
| American Samoa | |||||||
| Virgin Islands | |||||||
| Total | 7,622 | 100 | 2.3 | 3.6 | 4.3 | -46.5 | 74 |
Abbreviation NR = Non-Reporting Jurisdiction
*Percentages might not total 100% because of rounding
§ Cases per 100,000 population
¶New York State and New York City data are mutually exclusive
*Cases per 100,000 population
±Non-continental jurisdictions (i.e., Alaska, Hawaii, and U.S. territories) are not shown to scale and are not meant to depict their true geographic location.
¶New York State and New York City data are mutually exclusive.
| Characteristic | No. | Percent |
|---|---|---|
| Sex | ||
| Male | 3,733 | 49 |
| Female | 3,838 | 50.4 |
| Not reported as Male or Female; Missing | 51 | 0.7 |
| Race | ||
| American Indian or Alaska Native | 54 | 0.7 |
| Asian or Pacific Islander | 81 | 1.1 |
| Black | 563 | 7.4 |
| White | 5,266 | 69.1 |
| Other | 431 | 5.7 |
| Not Reported | 1,227 | 16.1 |
| Ethnicity | ||
| Hispanic or Latino | 570 | 7.5 |
| Not Hispanic or Latino | 5,086 | 66.7 |
| Not Reported | 1,966 | 25.8 |
| Total | 7,622 | 100.0 |
*Percentages might not total 100% because of rounding.
*Symptom onset date was available for 73.4% of cases (n= 5,623/7,622)
*Symptom onset date was available for 73.4% of cases (n= 5,623/7,662)
Territorial Jurisdictions = Puerto Rico only.
§Percentages might not total 100% because of rounding
*Cases per 100,000 population
§ Age data were available for 99.3% of reported cases (n=7,572/7,622)
*Cases per 100,000 population
§ Age and sex data were available for 98.7% of reported cases (n=7,525/7,622)
- Lawinger H, Hlavsa M, Miko S et al. Waterborne Disease and Outbreak Surveillance System (WBDOSS) Summary Report, United States, 2021. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC, 2023. https://www.cdc.gov/healthy-water-data/media/pdfs/2024/04/NORS-Water-2021-Annual-Summary_Final_11082023_1.pdf
- Arrowood M, Eberhard M, Gabrielli AF, et al. Cryptosporidiosis. In: Control of Communicable Diseases Manual, 21st Edition. Heymann DL, Ed. Washington, DC: 2022.
- Gharpure R, Perez A, Miller AD, Wikswo ME, Silver R, Hlavsa MC. Cryptosporidiosis outbreaks—United states, 2009–2017. MMWR Morb Mortal Wkly Rep 2019;68:568-572. DOI: http://dx.doi.org/10.15585/mmwr.mm6825a3
- 4. Collier SA, Deng L, Adam EA, et al. Estimate of burden and direct healthcare cost of infectious waterborne disease in the United States. Emerg Infect Dis 2021; 27:140. DOI: 10.3201/eid2701.190676.
- Abubakar II, Aliyu SH, Arumugam C, Hunter PR, Usman N. Prevention and treatment of cryptosporidiosis in immunocompromised patients. Cochrane Database of Systematic Reviews. 2007(1). DOI: 10.1002/14651858.CD004932.pub2
- CDC. Cryptosporidiosis: 1995 case definition. Atlanta, GA: US Department of Health and Human Services, CDC; 1995. Available at https://ndc.services.cdc.gov/case-definitions/cryptosporidiosis-1995/.
- CDC. Cryptosporidiosis: 2012 case definition. Atlanta, GA: US Department of Health and Human Services, CDC; 2012. Available at https://ndc.services.cdc.gov/case-definitions/cryptosporidiosis-2012/.
- US Census Bureau. American Community Survey 5-Year Data (2009-2019): Sex by Age Table (B01001) Population: April 1, 2009 to July 1, 2019. Washington, DC: US Census Bureau; Release Date: December 2020. Available at https://www.census.gov/data/developers/data-sets/acs-5year.html. Accessed using an Application Programming Interface on July 13, 2024.
- National Center for Health Statistics. Vintage 2020 postcensal estimates of the resident population of the United States (April 1, 2010, July 1, 2010–July 1, 2020), by year, county, single-year of age, bridged race, Hispanic origin, and sex. Prepared under a collaborative arrangement with the U.S. Census Bureau. Available from: http://www.cdc.gov/nchs/nvss/bridged_race.htm as of September 2021, following release by the U.S. Census Bureau of the unbridged Vintage 2020 postcensal estimates by 5-year age group on June 17, 2021. Accessed using an Application Programming Interface on July 13, 2024.
- US Census Bureau. Census Data API Discovery Tool. Washington, DC: US Census Bureau; Release Date: February 21, 2017. Accessed at https://www.census.gov/data/developers/updates/new-discovery-tool.html on July 13, 2024.
- Walker, K and Herman, M. tidycensus: Load US Census Boundary and Attribute Data as 'tidyverse' and 'sf'-Ready Data Frames. R package version 0.11. 2020. Available at https://CRAN.R-project.org/package=tidycensus.
- US Census Bureau. Census regions and divisions of the United States. Washington, DC: US Census Bureau. Available at https://www2.census.gov/geo/pdfs/maps-data/maps/reference/us_regdiv.pdf.