What Is a Coinfection?

A coinfection is a infection with two or more infectious organisms at once. Multiple infections can complicate treatment, although they may also provide an unexpected benefit to the patient, as sometimes one organism will suppress the growth of another. A doctor may suspect a coinfection on the basis of symptoms or risk factors, or direct test results showing the presence of multiple organisms in the patient. Viruses, bacteria, protozoans, worms, and other organisms can all be present simultaneously in a patient.

Two very common coinfections worldwide are human immunodeficiency virus (HIV) and hepatitis C virus (HCV), as well as HIV and tuberculosis. The risk factors for all three diseases are very similar, and patients who have one may also carry another. HIV and HCV, for example, are both passed through blood-to-blood contact, as seen among injection drug users. Patients can also host multiple bacterial infections as a result of untreated water or poor food hygiene.

The organisms involved in a coinfection typically interact with each other inside the patient. Sometimes they amplify each other and make the symptoms worse. The symptoms can also be confusing for care providers, as they may not immediately realize that the patient's symptoms are the result of multiple diseases, not just one. Other organisms may act against each other. Bacteria, for example, are often quite aggressive around other bacteria to protect their turf, and a coinfection may suppress the growth of one organism.

A doctor must consider coinfection in the process of developing a treatment plan. Medications can behave unexpectedly when multiple organisms are involved. The drug might suppress one organism and promote the growth of another, or allow a latent infection to flourish by killing off the secondary infection that was keeping it under control. Multi-drug protocols are often necessary, and it can be difficult for patients to comply with treatment when numerous drugs are involved, especially if the side effects are unpleasant or the drugs are expensive and the patient has trouble affording them.

Patients should make sure their doctors get a thorough medical history. Certain clues in a patient's recent history may provide evidence of coinfection and could be useful for a doctor to know about. Doctors need as much information as possible to decide what kinds of tests to order and how to proceed with treatment, and it is important to be aware that concealing evidence of coinfection out of shyness or worries about censure could result in getting the wrong treatment.