Objective: To examine the transmission of Cryptosporidium infection in households with an identified person with cryptosporidiosis.
Design: Prospective cohort study.
Setting: An urban slum in Fortaleza, Brazil.
Participants: Thirty-one households with a child less than 3 years of age (index case) who was positive for Cryptosporidium parvum using acid-fast and auramine-stained stool smears.
Measurements: Three stool samples (at 0, 2, and 6 weeks after identification of the index case) and two serum samples (0 and 6 weeks) were collected from each family member in households with an index case of Cryptosporidium infection.
Results: Forty-five percent of index cases of Cryptosporidium infection were associated with persistent (> 14 days) diarrhea. Secondary cases of Cryptosporidium infection were identified either by stool examination or seroconversion in 18 (58%) of 31 households involving 30 persons, yielding an overall transmission rate of 19%. Of the 202 persons in this study with at least one serum sample available for analysis, 191 (94.6%) had evidence of antibodies (either IgM or IgG) to Cryptosporidium.
Conclusions: Cryptosporidium parvum is highly transmissible and infective in the family setting, with transmission rates similar to other highly infectious enteric pathogens such as Shigella species. These data are cause for added concern because of the rapidly increasing rate of seropositivity for human immunodeficiency virus.
PIP: Between December 1990 and April 1992 investigators enrolled 31 households with a less than 3-year-old child infected with Cryptosporidium parvum in a prospective cohort study to determine the infectivity of Cryptosporidium parvum in families living in crowded conditions, mainly in the Goncalves Dias slum in Fortaleza, Brazil. The median household size was 7. The median age of the 33 index cases was 11 months, while the median age of the 192 family contacts was 21 years. 94% of the index cases had diarrhea at the time Cryptosporidium infection was diagnosed. 45% of the index cases had persistent diarrhea ( 14 days). The median duration of diarrhea was 14 days (range, 1-84 days). Most index cases (83%) had at least 1 other positive stool test for Cryptosporidium. Just 1 index case shed oocysts for 6 weeks. Index cases transmitted Cryptosporidium infection to 30 (19%) of 182 household contacts as evidenced by either a positive stool examination or seroconversion. These 30 secondary cases were from 18 of the 31 households. Only 8 (27%) secondary cases had diarrhea and 25% of them had persistent diarrhea, suggesting preexisting protective immunity in this area where Cryptosporidium infection is endemic. Household contacts who were 5 years old or younger were significantly more likely to have been diagnosed with Cryptosporidium than were those older than 5 years (30% vs. 5%; p 0.001). Most persons with at least 1 serum sample available for analysis (191/202 = 94.6%) had antibodies (IgM or IgG) to Cryptosporidium. The high rate of transmission of Cryptosporidium in this population, the serious threat of persistent diarrhea among young children, and the ever increasing rate of HIV transmission in Brazil (especially among slum dwellers with no access to condoms and to education about AIDS) should raise great concern.