Prevalence of Giardiasis

Giardiasis occurs worldwide but is more prevalent in areas with inadequate sanitary conditions and where water treatment facilities and procedures are sub par.¹ Unbeknownst to some, giardiasis is also found among people living in developed countries where sanitation is adequate and water supplies are piped and purified.² Worldwide, it is one of the most important non-viral infections causing diarrheal illness in humans.³ The highest prevalence of giardiasis occurs in the tropics and subtropics. In the United States, giardiasis is the most commonly reported pathogenic protozoan ≥ disease.⁴

Giardia Incidence, 2002¹⁰

Reported incidents per 100,000 population.

Prevalence rates range from 2-7% in developed countries and 20-30% in most developing countries. In 1987, U.S. state diagnostic laboratories found 7.2% prevalence in stool specimens. The CDC estimates that there are upwards of 2.5 million cases annually.⁵

Giardiasis is a common traveler's infection among tourists and business travelers to developing countries, namely the Soviet Union, Mexico, Southeast Asia, and western South America.⁶ One study of travelers to St. Petersburg, Russia reported a 95% incidence.¹ High infection rates have been reported in hikers and campers in the U.S. since these areas are inhabited by infected wild animals.⁷ Travelers represent one of the largest risk groups for giardiasis infection in the United States.⁸ A number of studies have reported an increased prevalence of giardiasis among homesexual men, as well.⁹