👉 A relay infection, also known as a secondary or superinfection, occurs when a new pathogen infects an already infected host by exploiting the compromised state of the primary infection. This can happen when the initial infection weakens the host's immune defenses, allowing another pathogen to take advantage and cause additional illness. For example, a person with a lung infection from tuberculosis might later develop a bacterial pneumonia caused by Streptococcus pneumoniae, as the weakened lungs struggle to fight off the new invader. Similarly, a viral infection like influenza can create an environment conducive to bacterial infections, such as Streptococcus pneumoniae or Staphylococcus aureus, complicating the overall health outcome.
