What are opportunistic infections?
People with advanced HIV infection are vulnerable to infections and malignancies that are called 'opportunistic infections' because they take advantage of the opportunity offered by a weakened immune system.
A partial list of the world's most common HIV-related opportunistic infections and diseases includes:
- Bacterial diseases such as tuberculosis, MAC, bacterial pneumonia and septicaemia (blood poisoning)
- Protozoal diseases such as PCP, toxoplasmosis, microsporidiosis, cryptosporidiosis, isopsoriasis and leishmaniasis
- Fungal diseases such as candidiasis, cryptococcosis and penicilliosis
- Viral diseases such as those caused by cytomegalovirus, herpes simplex and herpes zoster virus
- HIV-associated malignancies such as Kaposi's sarcoma, lymphoma and squamous cell carcinoma.
Different conditions typically occur at different stages of HIV infection. In early HIV disease people can develop tuberculosis, malaria, bacterial pneumonia, herpes zoster, staphylococcal skin infections and septicaemia. These are diseases that people with normal immune systems can also get, but with HIV they occur at a much higher rate. It also takes longer for a person with HIV to recover than it takes for someone with a healthy immune system.
When the immune system is very weak due to advanced HIV disease or AIDS, opportunistic infections such as PCP, toxoplasmosis and cryptococcosis develop. Some infections can spread to a number of different organs, which is known as 'disseminated' or 'systemic' disease. Many of the opportunistic infections that occur at this late stage can be fatal.
Why is there still a need to prevent and treat opportunistic infections?
Highly Active Antiretroviral Therapy (HAART) can reduce the amount of HIV in someone's body and restore their immune system. The introduction of HAART has dramatically reduced the incidence of opportunistic infections among HIV-positive people who have received the drugs. Yet the prevention and treatment of opportunistic infections remains essential.
Around the world, millions of people living with HIV in resource-poor communities have no access to HAART. And even where the drugs are available, they do not entirely remove the need for preventing and treating opportunistic infections. Sometimes it is advisable for people with acute opportunistic infections to begin HAART right away, especially if the infection is difficult to treat. However in certain cases it may be better to delay beginning HAART and instead only to administer treatment for the opportunistic infection, especially if there are concerns about drug interactions or overlapping drug toxicities.
Those who have already started taking antiretrovirals may require other drugs in certain circumstances. In particular, some opportunistic infections may be unmasked shortly after the beginning of HAART as the immune system starts to recover, and these may require specific treatment. Measures to prevent and treat opportunistic infections become essential if antiretrovirals stop working because of poor adherence, drug resistance or other factors.
Providing prevention and treatment of opportunistic infections not only helps HIV-positive people to live longer, healthier lives, but can also help prevent TB and other transmissible opportunistic infections from spreading to others.
Prevention of HIV-related opportunistic infections?
HIV-positive people can reduce their exposure to some of the germs that threaten their health. They should be especially careful around uncooked meat, domestic animals, human excrement and lake or river water. However there is no practical way to reduce exposure to the germs that cause candidiasis, MAC, bacterial pneumonia and other diseases because they are generally common in the environment.
Several HIV-related infections (including tuberculosis, bacterial pneumonia, malaria, septicaemia and PCP) can be prevented using drugs. This is known as drug prophylaxis. One particular drug called cotrimoxazole (also known as septra, bactrim and TMP-SMX) is effective at preventing a number of opportunistic infections. This drug is both cheap and widely available. The World Health Organisation (WHO) recommends that, in resource-limited settings, the following groups of people should begin taking cotrimoxazole:
- HIV-exposed infants and children, starting at 4-6 weeks after birth, or at first contact with health care, and continued until HIV infection is excluded.
- HIV-positive children less than 1 year old.
- HIV-positive children aged 1-4 years who have mild, advanced or severe symptoms of HIV disease, or a CD4 count below 25%.
- HIV-positive adults and adolescents who have mild, advanced or severe symptoms of HIV disease, or a CD4 count below 350 cells per ml.
- HIV-positive people with a history of treated PCP.
- According to WHO guidelines, treatment of HIV-positive people should continue until at least age 5, and in general should continue indefinitely, though it may sometimes be stopped following successful antiretroviral treatment.
Some of the worst affected countries may choose to treat all infants and children born to mothers confirmed or suspected of living with HIV, until HIV infection is excluded. They may also choose to treat everyone who is diagnosed with HIV, regardless of symptoms or CD4 count.
Drug prophylaxis is sometimes recommended even for those who have started HAART if they have very weak immune systems or are otherwise considered to be especially vulnerable. They may be advised to stop taking the drugs if their immune system recovers.
For people who have already contracted an opportunistic infection and undergone successful treatment, secondary prophylaxis may be advisable to prevent recurrence. This applies to diseases such as tuberculosis, salmonella, cryptococcosis and PCP.
Treatment of HIV-related opportunistic infections?
Some opportunistic infections are easier to treat than others. Effective treatment depends on health services being able to procure, store, select and administer the necessary drugs and to provide related treatment, care and diagnostic services to monitor health status and treatment response.
A few opportunistic infections and symptoms such as candidiasis of the mouth, throat or vagina (thrush), herpes zoster (shingles) and herpes simplex can be managed effectively through home-based care. In a home-based care setting diagnosis is made by observing symptoms.
Some opportunistic infections may be diagnosed by observation or using a microscope, and treated where there is minimal health infrastructure. Such infections include pulmonary tuberculosis and cryptococcal meningitis.
In a medium infrastructure setting, the facilities available include X-ray equipment and culture facilities. Using these, opportunistic infections such as extra-pulmonary tuberculosis, cryptosporidiosis, isopsoriasis, PCP and Kaposi's sarcoma can be diagnosed and treated.
Opportunistic infections such as toxoplasmosis, MAC and cytomegalovirus infection can be diagnosed and treated in places with advanced infrastructure. Treating these infections is often impossible in resource poor countries. Many developing countries lack the advanced equipment and infrastructure (such as CT scanning) needed to treat these more complex infections.
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