Cryptosporidiosis Outbreaks — United States, 2009–2017

Radhika Gharpure, DVM; Ariana Perez, MPH; Allison D. Miller, MPH; Mary E. Wikswo, MPH; Rachel Silver, MPH; Michele C. Hlavsa, MPH

Disclosures

Morbidity and Mortality Weekly Report. 2019;68(25):568-572. 

In This Article

Abstract and Introduction

Introduction

Cryptosporidium is a parasite that causes cryptosporidiosis, a profuse, watery diarrhea that can last up to 3 weeks in immunocompetent patients and can lead to life-threatening malnutrition and wasting in immunocompromised patients.* Fecal-oral transmission can occur by ingestion of contaminated recreational water, drinking water, or food, or through contact with infected persons or animals. For the period 2009–2017, public health officials from 40 states and Puerto Rico voluntarily reported 444 cryptosporidiosis outbreaks resulting in 7,465 cases. Exposure to treated recreational water (e.g., in pools and water playgrounds) was associated with 156 (35.1%) outbreaks resulting in 4,232 (56.7%) cases. Other predominant outbreak exposures included contact with cattle (65 outbreaks; 14.6%) and contact with infected persons in child care settings (57; 12.8%). The annual number of reported cryptosporidiosis outbreaks overall increased an average of approximately 13% per year over time. Reversing this trend will require dissemination of prevention messages to discourage swimming or attending child care while ill with diarrhea and encourage hand washing after contact with animals. Prevention and control measures can be optimized by improving understanding of Cryptosporidium transmission through regular analysis of systematically collected epidemiologic and molecular characterization data.

A cryptosporidiosis outbreak was defined as two or more cases epidemiologically linked to a common source by location and time of exposure. Public health officials in the 50 states, the District of Columbia, U.S. territories,§ and Freely Associated States voluntarily report outbreaks to CDC via the National Outbreak Reporting System (NORS). This report summarizes data from outbreak reports submitted to NORS by February 6, 2019, for which at least one etiology was Cryptosporidium and earliest illness onset date occurring during 2009 (the first year of NORS reporting) through 2017 (the most recent year for which data were available). NORS outbreak reports include data on etiology; counts of primary cases, hospitalizations, and deaths; transmission mode; exposures and settings; molecular characterization; and earliest illness onset date. Negative binomial regression analyses were conducted to assess trends in annual outbreak counts using SAS (version 9.4; SAS Institute).

For the period 2009–2017, public health officials from 40 states and Puerto Rico voluntarily reported to CDC 444 cryptosporidiosis outbreaks, resulting in 7,465 cases, 287 hospitalizations, and one death (Table). During this period, the eight Great Lake states** reported 254 (57.2%) cryptosporidiosis outbreaks, resulting in 3,335 (44.7%) cases (Figure 1). Exposure to treated recreational water was associated with 156 (35.1%) outbreaks, resulting in 4,232 (56.7%) cases and 183 (63.8%) hospitalizations. The most frequently implicated recreational water venues included pools (100 outbreaks; 64.1%), kiddie/wading pools (11; 7.1%), and water playgrounds (10; 6.4%). Twenty-three (14.7%) outbreaks were associated with multiple recreational water venues (e.g., multiple pools or water playgrounds). Among outbreaks associated with treated recreational water, the median case count was nine (range = 2–638). Among the 288 (64.9%) outbreaks not associated with treated recreational water, the median case count was five (range = 2–205).

Figure 1.

Reported cryptosporidiosis outbreaks (N = 444), by exposure jurisdiction* — United States, 2009–2017
Abbreviations: DC = District of Columbia; PR = Puerto Rico.
* Exposure jurisdictions are states, DC, and PR.
These numbers are largely dependent on public health capacity and reporting requirements, which vary across jurisdictions and do not necessarily indicate the actual occurrence of cryptosporidiosis outbreaks in a given jurisdiction.

Among all 444 outbreaks, 65 (14.6%) were associated with contact with cattle, resulting in 549 cases; 57 (12.8%) were associated with contact with infected persons in child care settings, resulting in 418 cases. Among the 22 foodborne outbreaks, nine (40.9%) were associated with unpasteurized milk and four (18.2%) with unpasteurized apple cider. The mode of transmission was unknown for 63 (14.2%) outbreaks; the predominant settings included private homes/residences (18; 28.6%) and child care (12; 19.0%). Molecular characterization data were available for 67 (15.1%) outbreaks, only one (1.5%) of which had unknown mode of transmission.

Negative binomial regression analysis indicated that during 2009–2017, the overall annual number of reported cryptosporidiosis outbreaks increased an average of 12.8% per year (95% confidence interval [CI] = 7.6%–18.0%) (Figure 2). The annual number of reported treated recreational water–associated outbreaks increased an average of 14.3% (95% CI = 3.4%–25.2%) per year during 2009–2016 (p = 0.010); however, because of a decline in reported outbreaks in 2017, no trend was found for the annual number of treated recreational water–associated outbreaks during 2009–2017 (p = 0.293). During 2009–2017, the annual number of reported outbreaks associated with contact with cattle increased an average of 20.3% (95% CI = 9.2%–31.4%) per year, and the annual number of reported outbreaks associated with contact with infected persons in child care settings increased an average of 19.7% (95% CI = 8.8%–30.5%) per year. During 2009–2017, the overall number of reported cryptosporidiosis outbreaks by month peaked during July–August, the number associated with treated recreational water peaked in June–August, the number associated with cattle contact peaked during March–May, and those associated with contact with infected persons in child care settings peaked during July–September (Figure 2).

Figure 2.

Reported cryptosporidiosis outbreaks (N = 444), by mode of transmission* and year of earliest illness onset date (A) and month of earliest illness onset date (B) — United States, 2009–2017
* Transmission modes were categorized as follows: Unknown if insufficient evidence to implicate one specific primary mode of transmission; Environmental contamination if transmitted through exposure to a contaminated environment not attributable to foodborne, waterborne, person-to-person, or animal contact transmission; Foodborne if transmitted by consumption of contaminated food or non-water beverages; Animal contact if transmitted through contact with animals or their living environments; Person-to-person if transmission occurred from direct contact with an infected person, their bodily fluids, or by contact with the local environment where the exposed person was simultaneously present; and Waterborne if transmission occurred via ingestion, inhalation, contact, or another exposure to water (e.g., treated or untreated recreational water, drinking water [including bottled water], or an environmental or indeterminate water source). https://www.cdc.gov/nors/forms.html.

* https://www.cdc.gov/parasites/crypto/index.html.
https://www.cdc.gov/nors/forms.html.
§ American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands.
Federated States of Micronesia, Marshall Islands, and Palau.
** Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin.

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