Pneumonia
The cough and the weight loss may also presage a serious infection caused by a germ that wouldn't bother you if your immune system was working properly.
"There are many different opportunistic infections and each one can present differently," Dr. Malvestutto says. In Ron's case, it was Pneumocystis pneumonia (PCP), aka "AIDS pneumonia," which eventually landed him in the hospital.
Other opportunistic infections include toxoplasmosis, a parasitic infection that affects the brain; a type of herpes virus called cytomegalovirus; and yeast infections such as thrush.