Interaction between viral and bacterial infections in the respiratory tract.

Interactions between different infectious agents often modify the outcome of an infection, compared to the course of infections caused by only a single agent. Virus infection in the respiratory tract influences several host defense factors and thereby paves the way for subsequent bacterial superinfection. Combined viral-bacterial infection aggravates the clinical disease and the final effect can often be defined as synergistic. Besides local defense factors such as mucociliary flow and bactericidal activity, which are modified by general viral factors, or the immunological response, direct interaction between bacteria and cells is also modified in some systems. An effect can be mediated by regulatory substances like interferons.