Pneumocystis pneumonia (PCP)

Pneumocystis pneumonia (PCP) is a lung disease caused by a common organism previously called Pneumocystis carinii , but which has now been renamed P. jiroveci . This was originally thought to be a protozoan, but more recently research has found that it is an atypical fungus. It is relatively common throughout the population and does not cause problems in people with healthy immune systems. However, if the immune system is damaged the organisms can grow in the lungs, causing PCP. In people with HIV, the organisms can also sometimes grow in other parts of the body such as the lymph nodes, bone marrow, spleen, liver and, occasionally, the eye. Illness caused by P. jiroveci is sometimes collectively described as pneumocystosis.

PCP was first noticed in children who were immunosuppressed because of malnourishment. People with HIV are potentially at risk from PCP if their CD4 cell count falls below 200 cells/mm3, although most cases occur among people with CD4 cell counts below 100 cells/mm3. PCP was a common cause of death among people with AIDS during the early years of the epidemic, and it is still one of the most common AIDS illnesses. However, treatment and prophylaxis for PCP have improved dramatically, and now it is much more unusual for PCP to be fatal.

Studies have also shown that HIV-positive smokers develop PCP two to three times faster than HIV-positive people who do not smoke. One study found, encouragingly, that ex-smokers who had given up at least a year before they entered the study seemed to develop PCP no quicker or more frequently than non-smokers. The researchers suggested that smoking may directly affect the immune cells in the lungs, activating HIV infected cells and reducing the ability of immune cells in the lung tissues and airways to combat infections.

Other factors which may increase a person's risk of PCP include gardening, breathing chemical irritants, previous pneumonia, camping and hiking.1

In the United Kingdom, there were 178 new cases of PCP in HIV-positive people in 2003, accounting for 28% of all AIDS diagnoses.

References

  1. Navin TR et al. Risk factors for community acquired pneumonia among persons infected with human immunodeficiency virus. Journal of Infectious Diseases 181(1): 158-164, 2000
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