Pneumocystis pneumonia (PCP): symptoms, risk groups and treatment

Pneumocystis jirovecii is an organism that shares characteristics with both fungi and protozoa. Patient.info's professional article says DNA studies suggest it is frequently found in healthy adults in the community, and that it can cause a transient infection in people with a normal immune system. Great Ormond Street Hospital describes it as an organism probably present in most people's lungs.

Problems arise when the immune system cannot keep the organism in check. Then it can cause pneumonia, called pneumocystis pneumonia and abbreviated PCP, or PJP using the newer species name. The infection was formerly called Pneumocystis carinii pneumonia, which is why you may still see PCP.

It is therefore an opportunistic infection: one that takes advantage of weakened immunity rather than infecting healthy people in the same way as ordinary bacterial pneumonia.

Patient.info lists several risk groups. They include HIV-positive people with a CD4 count below 200 cells/mm³, people taking steroids or other immunosuppressants, those with blood cancers, organ transplant recipients, people with connective tissue diseases such as rheumatoid arthritis, people with congenital immune deficiency, severe malnutrition and people with pre-existing lung disease.

It notes that the introduction of antiretroviral therapy dramatically reduced the incidence of PCP in people with HIV, while rates have been increasing in the HIV-negative susceptible population, which includes transplant recipients. A UK study of reported cases in England between 2000 and 2010 showed laboratory-confirmed cases increasing by 7% per year, principally in people without HIV, mainly immunocompromised transplant recipients or patients with blood cancers.

Great Ormond Street Hospital adds that children who are receiving long-term medicines that interfere with the body's ability to cope with infection may be more at risk.

Patient.info lists the typical features of PCP in adults. It also says the examination of the chest is often normal or only mildly abnormal, and that pulse oximetry may show low oxygen levels at rest.

• A cough, which is usually non-productive (dry), although a productive cough can occur in up to a third of people.

• Breathlessness on exertion.

• Fever.

• Rapid breathing.

• Chest pain.

• Signs of an underlying immune problem, for example oral thrush in a person with HIV.

Anyone who is known to have a weakened immune system and develops a new cough, fever or breathlessness should speak to their specialist team, GP or NHS 111 promptly, because early diagnosis greatly aids successful therapy. If someone is very short of breath or has chest pain, call 999 or go to A&E.

Great Ormond Street Hospital lists a raised temperature, rapid breathing and a dry cough as the symptoms in children. It advises families to tell the team about any new symptom, and to seek urgent help if signs of a severe allergic reaction to the medicine appear, such as difficulty breathing or chest pain.

Patient.info describes a combination of tests. A chest X-ray may be normal or show perihilar fluffy shadows or a pneumothorax. High-resolution CT is more sensitive than standard CT. Blood tests may show an elevated lactate dehydrogenase, which is suggestive but not specific, and blood gas measurements may show low oxygen.

The organism cannot be routinely cultured. It is detected by staining of sputum samples, and PCR-based methods have been developed. If sputum is negative but PCP is still suspected, bronchoscopy with a washing of the airways (bronchoalveolar lavage) or a lung biopsy may detect the organism. Doctors also consider other causes, including bacterial or viral pneumonia, tuberculosis, influenza and pulmonary embolism.

Patient.info says early diagnosis greatly aids successful therapy. Mild cases may be treated with oral medicines as outpatients, while moderate-to-severe cases usually require hospital admission and intravenous therapy.

Patient.info says co-trimoxazole side effects are numerous and include nausea, vomiting, skin reactions and changes in blood counts, and that adverse effects are more common in people with HIV. Great Ormond Street Hospital's medicine leaflet lists nausea and vomiting, bone marrow suppression (which can cause anaemia, easy bruising or bleeding and a higher risk of infection) and allergic reactions, and says blood counts are checked regularly.

The hospital advises reporting signs of a mild allergic reaction such as rash, itching or high temperature, and calling an ambulance at home for signs of a severe reaction such as difficulty breathing or chest pain. Patient.info says patients often deteriorate 3 to 5 days after starting treatment, thought to be due to inflammation caused by dead organisms, and that a favourable response may take seven days or more.

Patient.info says drug prophylaxis reduces the incidence of PCP and lengthens the disease-free intervals between episodes. It should be considered for all people with a history of the infection, severely immunocompromised patients, and HIV-positive people once the CD4 count falls below 200 cells/mm³. Co-trimoxazole by mouth is the drug of choice, given daily or on alternate days, and alternatives include inhaled pentamidine, dapsone and atovaquone.

Great Ormond Street Hospital notes that co-trimoxazole by mouth is usually given to prevent PCP, at lower doses than for treatment. Prophylaxis continues until immunity recovers sufficiently.

On the NHS, moderate-to-severe PCP is treated in hospital, as Patient.info describes. Preventive medicine is usually arranged by the team already looking after the underlying condition, such as HIV, transplant or haematology services.

Because it affects people with complex conditions, it is best for any additional private opinion to be shared with the NHS team responsible for immunosuppression or HIV care, so that medicines and prophylaxis are coordinated.