Cryptosporidiosis-related hospitalization in the US elderly population

The protozoan, Cryptosporidium spp., is a major cause of gastrointestinal illness worldwide. Though cryptosporidiosis has been a nationally notifiable disease in the USA since 1995, surveillance estimates are greatly undermined by failures to diagnose infection in the healthcare setting as well as report identified cases to health authorities. It is widely believed that immune senescence leads to enhanced vulnerability to cryptosporidiosis in the elderly, however this is not generally supported by surveillance data. The Centers for Medicare and Medicaid Services (CMS) databases present a novel means to investigate the burden of cryptosporidiosis in the elderly US population without the bias of underreporting. We abstracted all records (n=1304) containing a diagnosis of cryptosporidiosis-related (CR) illness in persons aged ≥65 years for the years 1991-2004. Annual rates of CR hospitalization were calculated and compared to surveillance data published by the CDC. Comorbidity and outcome of hospitalization was also assessed. CR hospitalizations increased during the study period, from 0.15 to 0.39 cases per 100,000 elderly per year, most likely due to increased awareness and testing. Comparison between the annual rates of CR hospitalization and CDC surveillance data revealed considerable state-to-state variation. Annual rates of CR hospitalization increased with age, such that the rate in persons aged >85 years more than doubled that in persons aged 65-74. Fluid and electrolyte imbalance was a common comorbidity while cancer was surprisingly infrequent. In-hospital death occurred in 5.4% of cases; the highest case fatality was in persons aged >85 (7.1%) and those with HIV (12.8%).