By Philip R. Fischer, MD, DTM&H

Professor of Pediatrics, Division of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN

Dr. Fischer reports no financial relationships relevant to this field of study.

SYNOPSIS: Almost all children in some parts of India have at least one Cryptosporidium infection during the first three years of life.

SOURCE: Kattula D, Jeyavelu N, Prabhakaran AD, et al. Natural history of cryptosporidiosis in a birth cohort in Southern India. Clin Infect Dis, published online Nov. 9, 2016.

Cryptosporidiosis is common (about 5 million episodes per year) and deadly (about 10,000 deaths per year) during the first two years of life in India. Affected children who survive are at risk of poor nutritional status and altered cognition. However, the natural history of this infection is not well known.

Thus, Kattula and colleagues prospectively evaluated diarrheal illnesses and stool pathogens in a cohort of 410 children in India from birth until 3 years of age. In the study area, HIV is rare (< 0.3% of pregnant women), and premature babies were excluded from the study. Stool was tested every two weeks and whenever diarrhea occurred. Anti-cryptosporidial serology was tested every six months.

Of the 497 children who were recruited, 410 completed the study. (Migration out of the area was the most common reason not to complete the study). During the three years of the study, 97% of children had at least one cryptosporidial infection. Cryptosporidium hominis was identified more commonly than Cryptosporidium parvum (73% vs. 17%). The overall incidence was 0.86 infections per year, with the first infection being identified at a median of 9 months of age. Two-thirds of infections were asymptomatic, but 9.4% of all diarrheal episodes were associated with Cryptosporidium in the stool. Most diarrheal episodes lasted two to four days. There was partial protection against subsequent infections, but only at a level of 69% protection after four infections.

The authors point out that the incidence of Cryptosporidium infection was higher in their study than has been found in other developing countries such as Peru, Guinea Bissau, Brazil, and Bangladesh. Some of the difference could have been due to the frequent monitoring of the Indian study subjects.


Cryptosporidiosis should not be considered uncommon or inconsequential. In many areas of the world, the infection occurs early, repeatedly, and symptomatically in many young children. Even immunocompetent children can suffer adverse consequences. Interestingly, and unlike in North America, C. parvum is less common than other Clostridium species among infected children in India.

Are Americans risk-free? Of course not. Human infection with Cryptosporidium was first documented in 1976, and many of us remember the Milwaukee outbreak of 1993 when municipal water supplies were contaminated and nearly half a million people were sickened.1

Investigators in Arizona recently evaluated recreational swimming habits of children and adults who frequented treated pools.2 Based on frequencies and durations of swimming times and based on reported water ingestion behaviors (splashing, drinking, spitting/spraying) and coupled with presumed levels of water contamination by Cryptosporidium, they calculated that children risk 2.9 Cryptosporidium infections per 100 swimmers per year, while adults risk 2.2 infections per 100 swimmers per year. The typical duration of chlorine exposure used to prevent contamination by pathogenic bacteria in swimming pools is inadequate to kill Cryptosporidium. Improved water purification combined with reminders to avoid getting pool water in the mouth should help reduce the risk of cryptosporidial infections.


  1. MacKenzie WR, Hoxie NJ, Proctor ME, et al. A massive outbreak in Milwaukee of cryptosporidium infection transmitted through the public water supply. N Engl J Med 1994;331:161-167.
  2. Suppes LM, Canales RA, Gerba CP, Reynolds KA. Cryptosporidium risk from swimming pool exposures. Int J Hyg Environ Health 2016;219:915-919.