Children are more likely than adults to be infected. Day care centers are often significant reservoirs of infection. Dogs may be carriers of the organism. Water is often a source of epidemics. The usual levels of chlorine used to purify water are insufficient to eradicate the parasite.
Water filtration is required.
Cyst excretion is irregular. Hence, several stool specimens may be required to diagnose Giardia in asymptomatic carriers. At times,diagnosis even requires small bowel biopsy. Assuming the presence of water filtration and the performance of routine careful handwashing in addition to the other steps listed in your letter,you appear to be doing the right things to minimize the transmission of Giardia in your home. Otherwise healthy children may pass the infective cysts for many months.