What is Pneumonia ?

Herpes simplex virus rarely causes pneumonia, except in groups such as: newborns, persons with cancer, transplant recipients, and people with significant burns.

People following organ transplantation or those otherwise-immunocompromised present high rates of cytomegalovirus pneumonia.

Those with viral infections may be secondarily infected with the bacteria Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae, particularly when other health problems are present.

Different viruses predominate at different periods of the year; during influenza season, for example, influenza may account for over half of all viral cases.

Outbreaks of other viruses also occasionally occur, including hantaviruses and coronavirus.

Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, immunosuppressive drugs, or other medical problems

It is most often caused by Histoplasma capsulatum, blastomyces, Cryptococcus neoformans, Pneumocystis jiroveci (pneumocystis pneumonia, or PCP), and Coccidioides immitis. Histoplasmosis is most common in the Mississippi River basin, and coccidioidomycosis is most common in the Southwestern United States.

The number of cases has been increasing in the later half of the 20th century due to increasing travel and rates of immunosuppression in the population.[39] For people infected with HIV/AIDS, PCP is a common opportunistic infection.