How common is toxoplasmosis?

Fairly. According to the CDC, about 60 million people in the US have this parasite in their body. Risk of getting sick increases in pregnancy or if immunity is low. People are exposed by eating undercooked vegetables or meat or from cat litter.
Not common in U.S. In the United States it is estimated that 23% of the population >12 years have been infected with toxoplasma gondii. In various places throughout the world, it has been shown that up to 95% of some populations have been infected. Infection is often highest in areas of the world that have hot, humid climates and lower altitudes (e.g. France). See cdc website for additional details.

Related Questions

How common is toxoplasmosis in humans from a cat? Cats tested positive for coccidiosis now I have flu like symptoms and fever.

See below. It would be more common for you to have cat scratch fever than the two you mention. However your symptoms are non specific and could be viral and not related at all to your cat only your physician can find out which it is. Read more...