Bacteria that cause pneumonia and meningitis are only able to spread when individuals are infected with flu, according to a new study.
The finding could have implications for the management of influenza pandemics and could help reduce incidence of pneumococcal infections in very young children, who are more susceptible to disease.
Streptococcus pneumoniae, the bacteria that causes both pneumonia and meningitis, usually lives harmlessly in the nasal passage.
It is already known that if a person is infected with influenza virus, the bacterium is more likely to spread to other parts of the body and may cause potentially life-threatening infections such as pneumonia, sepsis or meningitis.
Young children, the elderly and the immunocompromised are most vulnerable to these secondary bacterial infections.
Dimitri Diavatopoulos from the Radboud University Nijmegen Medical Centre in The Netherlands explained how infection with the flu virus is also necessary for transmitting S. pneumoniae between individuals.
His work has shown that in infant mice, all mice had to be infected with flu for pneumococcal bacteria to efficiently spread between them. Blocking influenza infection in these mice effectively prevented the spread of the bacterium.
Viral infection is likely to encourage the spread of pneumonia through a combination of factors, suggested Diavatopoulos.
"We think that the flu virus increases the bacterial load in the nose of colonized individuals but also makes uncolonized individuals more susceptible to pneumococcal infection by altering host immunity," he said.
Diavatopoulos believes that learning how viral infections affect not only the development but also the spread of bacterial pathogens will be clinically beneficial.
The finding was reported at the Society for General Microbiology's Spring Conference in Harrogate.