Distribution and Determinants of Waterborne Diseases in Michigan Subpopulations

BACKGROUND: The Intergovernmental Panel on Climate Change’s Fifth Assessment Report states that extreme precipitation events are expected to increase in the future, with consequent increases in waterborne disease (WBD) outbreaks. The four most commonly diagnosed WBD among Michigan hospitalized patients are cryptosporidiosis, giardiasis, Legionnaires’ Disease (LD), and non-tuberculosis mycobacterium infection (NTM). Populations at increased risk for these diseases include children, elderly, pregnant women, immunocompromised individuals, and those with certain comorbid conditions. We sought to identify frequent comorbid conditions and important risk factors for WBD to guide prevention efforts in Michigan.

METHODS: We queried ICD-9 codes in Michigan Inpatient Database (MIDB) records from 2009–2013 to identify hospitalizations with cryptosporidiosis (007.4), giardiasis (007.1), LD (482.84), or NTM (031.0 & 031.2) among the principal, secondary, and tertiary discharge diagnoses. Frequencies of non-WBD principal diagnoses and common comorbid conditions among hospitalized patients with WBD were calculated. We used Chi-Square tests to calculate relative risks of WBD among all hospitalized patients with one of five most frequent comorbid conditions or one of three most frequent non-WBD principal discharge diagnoses.

RESULTS: Of 6,499,219 hospitalizations, 2,105 (0.03%) met the WBD case definition: 222 cryptosporidiosis, 178 giardiasis, 881 LD, 818 NTM, and 6 with both cryptosporidiosis and giardiasis. The most frequent comorbid conditions among hospitalized patients with WBD were hypertension (37.1%), tobacco use (26.8%), hyperlipidemia (24.6%), hypokalemia (22.6%), and acute kidney failure (22%). A WBD was listed as principal diagnosis in 43.2% of WBD hospitalizations; when listed as secondary or tertiary diagnosis, the most common principal diagnoses were septicemia (30.5%), HIV infection (11%), and chronic obstructive pulmonary disease (COPD) (4.4%). HIV infection was the condition with the highest risk of WBD (relative risk [RR]: 36.8, 95% confidence interval [CI]: 31.4-43.3), including increased risk of cryptosporidiosis (RR: 67.9, CI: 46.3-99.7), NTM (RR: 66.0, CI: 53.8-80.9), giardiasis (RR: 51.6, CI: 23.1-82.9), and LD (RR: 3.1, CI: 1.4-6.9). Other comorbid conditions associated with WBD included septicemia (RR: 4.97, CI: 4.49-5.51), hypokalemia (RR: 3.12, CI: 2.82-3.46), COPD (RR: 2.38, CI: 2.05-2.76), acute kidney failure (RR: 2.32, CI: 2.09-2.57), and tobacco use (RR: 1.87, CI: 1.69-2.06).

CONCLUSIONS: Hospitalization data proved useful for identifying WBD vulnerabilities. Conditions with increased risk of WBD included COPD, tobacco use, and particularly HIV infection, which demonstrated increased risk of all four WBD individually. With future climate change-related increases in WBD outbreaks anticipated, education and prevention efforts should target populations most vulnerable to ensure their health and safety.