Increasingly, the microorganisms that cause pulmonary infections are fungi. Although still much rarer than bacterial lung infections, fungal pneumonias have shown a remarkable rise in incidence. One hospital in the Midwest reported an overall 20-fold increase in fungal infections (of all types) in the 10 years between the late 1970s and the late 1980s. And a great many of those infections occur in the lungs. As you read in chapter 5, two broad categories of fungi cause human infections: those considered to be primary pathogens, which readily cause disease even in healthy hosts, and opportunists, which cause disease primarily in hosts that are weakened due to underlying illness, advanced age, immune deficiency, or chemotherapy of some sort