Giardiasis surveillance--United States, 1998-2002

Giardiasis, a gastrointestinal illness, is caused by the protozoan parasite Giardia intestinalis.1998-2002.State, commonwealth, territorial, and two metropolitan health departments voluntarily reported cases of giardiasis through CDC's National Electronic Telecommunications System for Surveillance.During 1998-2002, the total number of reported cases of giardiasis decreased from 24,226 for 1998 to 19,708 for 2001 and then increased to 21,300 for 2002. The number of states reporting giardiasis cases increased from 42 to 46; however, the number of states reporting more than 15 cases per 100,000 population decreased from 10 to five. A greater number of case reports were received for children aged 1-9 years and for adults aged 30-39 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.The increase observed for 2002 might reflect increased reporting after reporting of giardiasis as a nationally notifiable disease began in 2002. Transmission of giardiasis occurs throughout the United States, with increased 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 might reflect increased use of communal swimming venues (e.g., lakes, rivers, swimming pools, and water parks) by young children.Giardiasis surveillance provides data to educate public health practitioners and health-care providers about the epidemiologic characteristics and the disease burden of giardiasis in the United States. These data are used to improve reporting of cases, plan prevention efforts, and establish research priorities.