Abstract
Background: Giardia lamblia is the most common intestinal parasite in the most parts of Iran, including Hamadan. Treatment of healthy cyst passers is a controversial challenge in view of public health features. The aim of this study was to determine the reinfection rate of G. lamblia after treatment during one year follow up.
Methods: In the endemic area for giardiasis, Hamadan, the west of Iran, 87 individuals out of 120 school children cyst passers, aged between 7-14 years were effectively treated for G. lamblia with metronidazole. Stools were examined monthly in a period of 12 months after treatment, to determine the rate of reinfection. Eighty seven children were eligible to analysis after one year follow up.
Results: Totally 83% of children were reinfected within 12 months, and reinfection rate was significantly higher than the second six months during first half of study, i.e, October through March (P < 0.05). The cumulative rate of reinfection with this parasite was almost linear. No significant association observed between the age and sex of the children and duration of parasite elimination after treatment, but reinfection rate in some parts of the city was significantly higher and occurred sooner than the other parts (P < 0.001).
 Conclusion: We concluded that, reinfection rate for G. lamblia was rapid and high in this area. Treatment of all symptomless G. lamblia infections in a hyper endemic region of a developing country is of questionable value because of rapid reinfection.