During 2012, 633 cases of Giardia infection (11.8 per 100,000) were reported. This represents a 28% decrease from the median number of cases reported annually from 2002 through 2011 (median, 878 cases; range, 678 to 1,378). Historically, a substantial proportion of Giardia cases have represented positive tests during routine screenings of recent immigrants and refugees. The median age for all case-patients reported in 2012 was 26 years (range, 4 weeks to 92 years). Fifteen percent of cases were less than 5 years of age, and 22% of cases were over 50 years of age.
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