Pneumocystis is an organism that has changed name and species over the past few years: Originally called “Pneumocystis carinii”, and thought to be a protozoa, it was discovered that it is in fact a fungus and should correctly be referred to as “pneumocystis jirovecii”. The infection cause is however still referred to pneumocystis pneumonia and retains the abbreviation of PCP.
Before the emergence of the HIV epidemic, PCP was only seen patients who had badly suppressed immunity, for example people on immunosuppressive drugs after a transplant, or patients receiving chemotherapy. Since the advent of the HIV epidemic it is very common in advanced HIV disease and is considered to be an AIDS-defining illness. People with HIV infection usually become susceptible to pneumocystis jirovecii infection when their CD4 cell count falls below 200cells/ul. This usually takes the form of a respiratory infection (pneumonia). In many people this will be the first illness that marks the onset of Aids and around 80% of people with AIDS will get PCP at some stage. People whose immune systems have been suppressed for reasons other than HIV infection continue to get PCP. The majority of cases of PCP are however now seen in people with AIDS.
The risk of transmitting PCP from one person to another is considered to be very small. It is thought that people who get PCP acquire the organism either from an environmental source, or have been carrying the organism for a while, and become ill once they become susceptible. However, there is still some debate around the topic of how exactly people acquire the pneumocystis organism.
Symptoms and signs of PCP
The most common symptoms of PCP are gradual onset of shortness of breath with cough, fever and tiredness. The cough is usually dry (without sputum production).
Physical examination is characterised by a rapid respiratory rate (fast breathing), fever and frequently very little additional sounds observed when listening to the chest. Low oxygen concentrations are also frequently observed.
How is PCP diagnosed?
If pneumonia is suspected, your doctor will order tests to help determine its severity. A chest X-ray may show a typical pattern of widespread fluffy patches in the lungs, known as "diffuse infiltrates". However the CXR may also be normal. Tests to measure oxygen levels in the blood will be low and are related to the severity of the infection. If the result of the finger probe “oximeter” is abnormal, you may also need a test of arterial blood gases (ABG), in which a sample of blood is drawn from a wrist or thigh artery and sent to the laboratory for analysis. If your oxygen level is very low, you will most likely require hospitalisation.
Many conditions that affect the lungs, including asthma, bronchitis, other types of pneumonia, and tuberculosis, may produce symptoms similar to PCP. To make sure the problem is PCP, your doctor will ask you to cough up a sample of sputum, which will be examined in the laboratory. Your doctor may arrange for you to have an induced sputum test. For this test, you are asked to inhale a salt water vapor to stimulate vigorous coughing that produces sputum from deep in the lungs. If induced sputum does not reveal Pneumocystis organisms, it may be necessary to perform a bronchoscopy with lavage, where a tube is inserted into the lungs to obtain a sputum sample.
The sputum will be sent to the laboratory to be examined under a microscope to see if the Pneumocystis organisms are present. However, even if they are present, they are not very easy to observe under the microscope. Other methods of detecting the organism in sputum are being investigated, such as using the polymerase chain reaction (PCR) to detect the DNA of the organism. This is still largely experimental, but some results are promising.
It can be difficult to get a sputum sample from a person with PCP, and the tests to identify the fungus may not be available in all hospitals. Since PCP is a serious condition, a person with Aids will often be treated for PCP, based on their symptoms alone, i.e. without conclusively confirming the diagnosis.
How is PCP treated?
PCP is usually treated with the medication co-trimoxazole (“Bactrim”, “Septran”, “Purbac”), which is usually given orally in all but the most severe cases when it can be given via a drip. (In people who are allergic to co-trimoxazole, a combination of clindamycin and primaquine may be used.) In severe cases of PCP, prednisone (cortisone) may be added to reduce inflammation in the lungs. Treatment usually lasts for 14 – 21 days. Severe PCP requires hospitalisation, and patients with very low oxygen levels will need supplementary oxygen by facemask or even via a ventilator.
Anyone who has had a first episode of PCP, after completing the acute treatment, must remain on co-trimoxazole to prevent recurrences. Anti-retroviral drugs (ARVs) are now indicated for anyone with a CD4 count of less than 350 in addition to anyone who has had an AIDS related illness such as PCP. Your doctor will generally wait until you have recovered before starting ARVs. Once you have been established on ARVs and your CD4 count has been stabilised above 200, the co-trimoxazole therapy may be safely discontinued.
Even with the best possible treatment, about one in five people with severe PCP may die.
What can I do to prevent PCP?
Anyone with a CD4 cell count below 200/ul is at risk for PCP, and should take daily co-trimoxazole to help prevent it. Starting anti retroviral therapy earlier at a CD4 count of 350 will reduce your chances of getting PCP.
Preventive treatment (prophylaxis) can generally be safely discontinued once on ARVs, when your CD4 count rises above 200/ul and is stable for over three months.
Previously reviewed by Dr Andrew Whitelaw, MBBCh (Witwatersrand), MSc (UCT), FCPath (Micro) (SA), Clinical Microbiologist, Department of Microbiology, University of Cape Town and Groote Schuur Hospital
Revised by Richard van Zyl-Smit ,MBCHB, MRCP(UK), DIP HIV Man (SA), FCP(SA) Cert Pulm (SA), Specialist Physician and Pulmonologist, Division of Pulmonology and UCT Lung Institute, Department of Medicine, University of Cape Town, (October 2010)