By Robert Preidt
WEDNESDAY, July 15, 2015 (HealthDay News) -- Viruses cause more pneumonia-related hospitalizations among American adults than bacteria, although the cause of the lung infection is undetected in most cases, a new federal study says.
The findings show the need for improved diagnostic tests, according to Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, which conducted the study.
"Pneumonia is a leading cause of hospitalization and death among adults in the United States and in 2011 the medical costs exceeded $10 billion," he said in a CDC news release.
"Most of the time doctors are unable to pinpoint a specific cause of pneumonia. We urgently need more sensitive, rapid tests to identify causes of pneumonia and to promote better treatment," Frieden said.
CDC researchers looked at more than 2,300 adults, whose median age was 57. All were treated for pneumonia at three hospitals in Chicago and two hospitals in Nashville between January 2010 and June 2012.
Viruses were detected in 27 percent of the patients and bacteria in 14 percent of the patients, the study found. Human rhinovirus (HRV) was the most commonly detected virus. Influenza was the second most common type of virus, the researchers said.
Influenza was the cause of pneumonia in twice as many patients 80 and older than any other type of virus except HRV, the study revealed. This finding highlights the need for increased flu vaccine use and effectiveness in this age group, the researchers said.
Streptococcus pneumoniae was the most common type of bacteria found in patients. It caused five times more pneumonia hospitalizations among adults 65 and older than in younger adults, the researchers noted.
S. pneumoniae, Staphylococcus aureus and Enterobacteriaceae bacteria were common among severely ill patients, and were detected in 16 percent of intensive care unit patients, compared with 6 percent of non-ICU patients, the study found.
Results of the study were published July 14 in the New England Journal of Medicine.
The study's lead author, Dr. Seema Jain, a medical epidemiologist in the CDC's Influenza Division, said the study found more viruses in people with pneumonia than expected. Jain said better testing may be one reason why. Vaccines for bacterial causes of pneumonia may be another reason, Jain suggested in the news release.
"However, what's most remarkable is that despite how hard we looked for pathogens (germs), no discernible pathogen was detected in 62 percent of adults hospitalized with pneumonia in the ... study. This illustrates the need for more sensitive diagnostic methods that can both help guide treatment at the individual level as well as inform public health policy for adult pneumonia at a population level," Jain said.