Problem/condition: Giardiasis is a nationally notifiable gastrointestinal illness caused by the protozoan parasite Giardia intestinalis.
Reporting period: 2006-2008.
System description: State, commonwealth, territorial, and two metropolitan health departments voluntarily report cases of giardiasis through CDC's National Notifiable Disease Surveillance System.
Results: During 2006--2008, the total number of reported cases of giardiasis increased slightly from 19,239 for 2006 to 19,794 for 2007 and decreased slightly to 19,140 for 2008. During this period, 49 jurisdictions reported giardiasis cases; giardiasis is a reportable condition in 45 states (not reportable in Indiana, Kentucky, Mississippi, North Carolina, and Texas). A greater number of case reports were received for children aged 1-9 years and for adults aged 35-44 years compared with other age groups. Incidence of giardiasis was highest in northern states. Peak onset of illness occurred annually during early summer through early fall.
Interpretation: Transmission of giardiasis occurs throughout the United States, with more frequent diagnosis or reporting occurring in northern states. However, state incidence figures should be compared with caution because individual state surveillance systems have varying capabilities to detect cases. The seasonal peak in age-specific case reports coincides with the summer recreational water season and likely reflects increased outdoor activities and exposures such as camping and use of communal swimming venues (e.g., lakes, rivers, swimming pools, and water parks) by young children.
Public health action: Local and state health departments can use giardiasis surveillance data to better understand the epidemiologic characteristics and the disease burden of giardiasis in the United States, design efforts to prevent the spread of disease, and establish research priorities.