RESUMEN
Six percent of 9, 856 fecal specimens from 4, 928 patients from all states and the District of Columbia tested positive for Cryptosporidium parvum infections in 2003-2005. Annual prevalence rate was similar in all three years. Overall prevalence was lowest in winter months but peaked in May, especially in males that were relatively more frequently infected than females. Additional peaks were observed in September, 2003 and February, 2004. Frequency of infection increased with age in both sexes up to age 80-89. Twenty two percent of infected patients were asymptomatic. Intestinal symptoms were relatively more common than extra-intestinal symptoms. Singly infected males [82%] and females [77%] experienced one or more of 17 intestinal symptoms [most frequently diarrhea, bloating, and gas] and one or more of 19 extra-intestinal symptoms [most frequently fatigue, brain fog and neurological problems]