What is the most likely way humans are exposed to Q fever?

Humans are most likely exposed to Q fever primarily through aerosol contact with infected animals. This is due to the nature of the bacteria that cause Q fever, Coxiella burnetii, which are commonly found in livestock, particularly sheep, goats, and cattle. The bacteria can be present in various secretions from infected animals, including urine, feces, and especially in the birth products of these animals, which can become aerosolized. When inhaled, this contaminated aerosol can lead to respiratory infection and subsequently result in Q fever.

In contrast, while the other exposure routes presented in the options—such as consumption of contaminated water, direct skin contact, and ingesting undercooked meat—can present risks for other pathogens, they are not the primary means of Q fever transmission. Therefore, understanding the primary route of aerosol transmission is essential for effective prevention and control of this infection in at-risk populations.