Background: Blastocystis infection is one of the most common intestinal protozoan infections reported in Thai population of all age groups for which epidemiological information is important to understand patterns of transmission for developing methods of prevention and control for each specific group. The authors aimed to study prevalence, incidence and risk factors associated with Blastocystis infection in orphans and childcare workers. Additionally, subtypes of Blastocystis were identified.
Material and Method: A retrospective cohort study of Blastocystis sp. was conducted in orphans aged less than 5 years and their childcare workers at Babies’ Home, Nonthaburi Province, Thailand. A base line survey was conducted in December 2009 and a follow-up survey was conducted in April 2010. A total of 336 and 331 stool samples were collected. Blastocystis infection was examined using short-term in vitro cultivation in Jones’s medium supplemented with 10% fetal calf serum. To analyze subtypes of Blastocystis sp., PCR-RFLP of the small subunit ribosomal RNA gene was performed.
Results: The prevalence of Blastocystis infection in December 2009 and April 2010 were 8.1% and 13.3%, respectively. The incidence rate of Blastocystis infection was 1.6/100 person-months. Subtype analysis of Blastocystis sp. in December 2009 and in April 2010 showed that subtype 3 was the most predominant (76% and 76%), followed by subtype 1 (16% and 20%), and unidentified subtype (8% and 4%), respectively. Subtype 3 is of human origin, thus person-to-person transmission is considered a major route of Blastocystis infection in this population.
Conclusion: Person-to-person transmission of Blastocystis infection in orphans living in the same house had been proposed, thus the prevalence and incidence of Blastocystis infection could be used to reflect the hygienic condition in the orphanage. Infection prevention and control practice can be effectively implemented.

Keywords: Blastocystis infection, Blastocystis sp., Subtype, Orphans