Viral and Bacterial Infections in Lungs May Promote IPF

Respiratory viral and bacterial infections are common in people with idiopathic pulmonary fibrosis (IPF) and might play a role in the development of the disease, a study reported.

The study, “The role of viral and bacterial infections in the pathogenesis of IPF: a systematic review and meta-analysis,” was published in the journal Respiratory Research.

The lungs are directly exposed to airborne germs, and previous studies have suggested that germs, such as viruses and bacteria, are important contributors to IPF onset.

Researchers in Iran, for this reason, investigated the prevalence of viral and bacterial infections in IPF patients, and the possible association between these respiratory infections and IPF.

Using a method of analysis that combines the results of multiple studies — a systematic literature review and meta-analysis — the researchers collected information from 32 studies involving a total of 2,203 people with IPF (ages 26 to 87) from various locations around the world.

Among the patient group analyzed, 53.72% had viral infections and 31.21% had bacterial infections.

Viral and bacterial infections were more common in patients from the U.S. (86.9%) and Japan (73.1%), and less common in those residing in the U.K. (5%) and South Korea (1.5%).

“Geographical variations might explain the inconsistent results that [are] present in the studies,” the researchers wrote.

While the geographic distribution of the samples was wide, the results might not be “applicable to other patient populations,” they added.

Another point raised by the team was the use of different methods to sample and detect viruses and bacteria in these studies, which could have contributed further to the disparity across countries.

The most prevalent viruses found in the IPF patients analyzed were the herpes simplex virus (HSV; 77.7%) and Epstein-Barr virus (EBV; 72.02%).  The least prevalent was Influenza A (7.3%). Among bacterial sources of infection, the most prevalent were related to the Streptococcus species (99.49%), while Raoultella (1.2%) had the lowest prevalence.

Aging has been linked to IPF progression. Accordingly, the researchers also looked into how age might affect the relationship between respiratory infections and IPF. However, they found that viral and bacterial infections were less common in older patients than in younger ones.

It is thought that viral and bacterial infections are involved in both the initiation and progression of IPF, possibly by disturbing innate immunity — the immune system’s non-specific, first line of defense from invasion by germs — and increasing inflammation.

“Our study supports the hypothesis that respiratory infection could play a key role in the pathogenesis of IPF,” the researchers concluded, adding that “the presence of viral and bacterial infections is a risk factor” for the disease.

The team noted, however that, given the study’s small sample size and the fact that germ types might be specific to certain geographical areas, “the association between viral infection and acute exacerbation of IPF requires further investigation.”