What is the prevalence of parasitic infections among adults in the United States?

Prevalence of Parasitic Infections in US Adults

The overall prevalence of parasitic infections among adults in the United States is relatively low compared to endemic regions, with the most common parasites being Toxoplasma gondii (affecting approximately 12.4% of the population over age 6 as of 2009-2010), Giardia, and Cryptosporidium, though most infections occur in specific high-risk populations including immigrants, travelers, and immunocompromised individuals. 1, 2

Key Epidemiological Data

Toxoplasmosis

• The age-adjusted seroprevalence of Toxoplasma gondii among the general US population over 6 years old was 12.4% in 2009-2010, representing a decline from 15% in 1988-1994 1
• Among women of childbearing age (15-44 years), seroprevalence was only 9.1% in 2009-2010, down from 15% in 1988-1994 1
• For US-born women of childbearing age specifically, the rate was even lower at 6% in 2009-2010 1
• Population-based estimates suggest T. gondii infects approximately 1.1 million people annually in the United States 1
• People born outside the United States have significantly higher seroprevalence (25.1%) compared to US-born individuals (9.6%) 1

Intestinal Parasites

• Giardiasis, cryptosporidiosis, and cyclosporiasis are nationally notifiable conditions in the United States 3
• Cryptosporidiosis has been reported in 3-4% of HIV-infected children in the United States 1
• Pinworm is the most common intestinal parasite in US children, though it is not a notifiable infection 3

Tickborne Parasitic Infections

• Anaplasmosis has an average annual incidence of 6.3 cases per million persons based on 2008-2012 surveillance data 1
• Babesiosis occurs primarily in the same geographic regions as Lyme disease in the northeastern and upper Midwestern states 1

High-Risk Populations

Immigrants and Travelers

• Parasitic infections in the United States are predominantly seen in immigrants and travelers returning from endemic regions 2
• Nearly 2,000 cases of imported malaria are diagnosed annually in the United States 2
• Chagas disease, cysticercosis, and toxoplasmosis affect millions in the United States and are considered neglected parasitic diseases 4

Geographic and Demographic Risk Factors

• Toxoplasmosis seroprevalence is higher in the Northeast (29.2%) compared to the South (22.8%), Midwest (20.5%), or West (17.5%) 5
• Hispanic individuals have higher seroprevalence (15.8%) compared to non-Hispanic whites (10.2%) 1
• Risk increases with foreign birth, lower educational level, crowded living conditions, and soil-related occupations 5

Immunocompromised Individuals

• HIV-infected individuals are at higher risk for severe manifestations of parasitic infections including toxoplasmosis, cryptosporidiosis, and microsporidiosis 1
• Strongyloidiasis can cause life-threatening hyperinfection syndrome in patients receiving corticosteroids or other immunosuppressive therapy 2

Clinical Implications

Underdiagnosis Concerns

• Pulmonary and intensive care physicians often fail to consider parasitic disease, resulting in delayed diagnosis and adverse outcomes 2
• Chronic strongyloidiasis causes few symptoms and can persist for decades after leaving endemic regions, making it easily missed 2
• Most symptoms of parasitic infections are nonspecific, and many infected individuals remain asymptomatic 6

Geographic Considerations for Specific Parasites

• Paragonimus is endemic not only in East Asia but also Southeast Asia, West Africa, the Pacific coast of Latin America, and North America 2
• Alpha-gal syndrome from Lone Star tick bites occurs primarily in the Southeast, Mid-Atlantic, Midwest, and East Central United States 7

Common Pitfalls

• The declining seroprevalence of toxoplasmosis means that approximately 91% of US women of childbearing age remain susceptible to acute infection during pregnancy 1
• Neurocysticercosis accounts for 2.1% of all emergency department visits for seizures in the United States, yet it remains underrecognized 4
• Intestinal parasites should be suspected in anyone presenting with diarrhea lasting more than 7 days, regardless of travel history 3