Coinfections

Coinfections refer to the simultaneous or sequential infection of a single host by two or more distinct pathogens. They can arise when multiple infectious agents are present in the same environment or when one infection alters the host’s immune defenses, making another infection more likely. Interactions between pathogens may be synergistic, worsening disease severity or progression, or antagonistic, where one infection impairs the other. The clinical course of a coinfection can differ from that of a single infection due to these interactions and the host’s immune state.

Common examples include HIV co-infection with tuberculosis, where immunosuppression increases TB risk and TB can accelerate HIV progression; viral-bacterial combinations such as influenza with Streptococcus pneumoniae or Staphylococcus aureus can lead to more severe pneumonia; malaria frequently coexists with helminth infections, particularly in tropical regions, which can influence anemia and immune responses; viral coinfections with hepatitis B or C are also seen in susceptible populations. In immunocompromised patients, such as those with HIV or after organ transplantation, opportunities for opportunistic coinfections are higher.

Clinical implications include diagnostic complexity due to overlapping symptoms and limitations of laboratory tests, and treatment considerations such as the need to address multiple pathogens simultaneously, potential drug interactions, and effects on immune recovery and vaccine responses. Epidemiologically, coinfections are more common in settings with high prevalence of multiple pathogens and can be influenced by social and environmental factors, leading to syndemic dynamics that shape public health strategies.