Soil-transmitted helminth infections
2026 Case Definition

Clinical Criteria

• In the absence of a more likely diagnosis, an individual with at least one of the following manifestations: abdominal discomfort and/or pain, iron-deficiency anemia or anemia of chronic disease, malabsorption, malnutrition, hypoproteinemia, malaise, weakness, diarrhea, colitis, or rectal prolapse.

Laboratory Criteria

Confirmatory Laboratory Evidence:

• Detection of Ascaris species, Trichuris species, Ancylostoma species, or Necator species eggs in stool by ova and parasite exam, OR
• Visual evidence of helminths (larval or adult stage) in a human tissue (e.g., histological sample), clinical specimen (e.g., bronchoalveolar lavage), body system (e.g., colonoscopy or endoscopy), or passed in stool that have been identified as a soil-transmitted helminth (STH) species (Ascaris lumbricoides/suum, Trichuris trichiura, Ancylostoma duodenale, or Necator americanus).

Presumptive Laboratory Evidence:

• Detection of DNA from Ascaris lumbricoides/suum, Trichuris trichiura, Ancylostoma duodenale, or Necator americanus by molecular methods performed on stool.

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

Criteria to Distinguish a New Case from an Existing Case

A new case of STH infection should be enumerated only:

• If a person was not previously enumerated as a case of STH infection caused by the same species as determined by laboratory evidence in the past 12 months,* OR
• If previously enumerated as a case within the past 12 months, evidence shows that the person received appropriate treatment for that specific STH infection.

^* Lifespan of the adult worms and viability of eggs in the environment:

• For Trichuris trichiura, adult worms live in a human host about one to two years. Eggs are viable in some environments for up to 6 years.
• For Ascaris lumbricoides, adult worms live in a human host for about one year. Eggs are viable in some environments for up to 15 years.
• For Ancylostoma duodenale, adult worms live in a human host for up to 3 years, although most adults survive an average of 6 months. For Necator americanus, adult worms live in a human host for an average of one to 5 years with a maximum lifespan of 18 years. Hookworm eggs are viable in some environments for several months.

Note: If concurrently infected with more than one species, each species should be enumerated as its own case.

Probable

• Meets clinical criteria AND
  • Meets presumptive laboratory evidence for:
    • Ascaris species (ascariasis), OR
    • Trichuris species (trichuriasis), OR
    • Ancylostoma species or Necator species (intestinal hookworm disease), OR
  • Meets vital records criteria^‡ for:
    • Ascariasis, OR
    • Trichuriasis, OR
    • Intestinal hookworm disease.

^‡ Ascariasis, trichuriasis, or intestinal hookworm disease listed as a cause of death or a significant condition contributing to death on a death certificate.

Confirmed

• Meets confirmatory laboratory evidence for:
  • Ascaris species (ascariasis), OR
  • Trichuris species (trichuriasis), OR
  • Ancylostoma species or Necator species (intestinal hookworm disease).