What might be a common source of protozoan infections in humans?

Contaminated water is indeed a common source of protozoan infections in humans. Water can become contaminated with various protozoa, such as Giardia lamblia or Entamoeba histolytica, through fecal contamination. This occurs when sewage or animal waste containing these pathogens is introduced into drinking water supplies or natural water sources.

Ingestion of contaminated water can lead to gastrointestinal illnesses, which are some of the main health concerns associated with protozoan infections. The risk is particularly high in areas lacking proper sanitation and where water treatment facilities may be inadequate.

While raw vegetables can also carry protozoa if washed with contaminated water, direct contact with infected individuals and airborne particles are less common transmission routes for protozoan infections. Therefore, contaminated water stands out as the primary and most significant source.