Cryptosporidiosis in the elderly population of the United States.

BACKGROUND

Although cryptosporidiosis has been a nationally notifiable disease since 1995, surveillance estimates are undermined by limited diagnostic testing and incomplete reporting of cases to health authorities. Further, existing surveillance systems do not capture the specific risks of cryptosporidiosis to sensitive populations, such as the elderly population. The Centers for Medicare and Medicaid Services databases present a novel means to investigate the cryptosporidiosis burden in the US elderly population.

METHODS

We abstracted records for all Medicare-covered persons aged >or= 65 years who received a diagnosis of a cryptosporidiosis-related illness between 1991 and 2004 (n = 1304) in the United States. Annual rates of cryptosporidiosis-related hospitalization were calculated and compared with surveillance data published by the Centers for Disease Control and Prevention. The total burden of disease and outcomes of hospitalization were also assessed.

RESULTS

Cryptosporidiosis-related hospitalizations increased during the study period at a rate of 0.15-0.39 cases per 100,000 elderly persons each year; this increase was probably attributable to increased awareness and testing. Comparison between cryptosporidiosis-related hospitalization and Centers for Disease Control and Prevention surveillance data revealed considerable state-to-state variation. The rate of hospitalization among persons aged >or= 85 years was more than double that among persons aged 65-74 years. Volume depletion and noninfectious diseases of the digestive system were common concurrent diagnoses. The highest case-fatality rates were among persons aged >or= 85 years (7.8%) and among persons infected with HIV (10.3%).

CONCLUSIONS

Although awareness of cryptosporidiosis has increased, underdiagnosis and underreporting of cases remains a major barrier to accurate surveillance in many states. Infection among elderly persons is associated with volume depletion and negative hospital outcomes, including death.