Bacteria And Viruses Can Cause Pneumonia

September 1, 2019

CHICAGO – A new study suggests that pneumonia caused by bacterial infections poses a greater threat to the heart than pneumonia caused by viral infections.

Researchers found that patients diagnosed with bacterial pneumonia in the study had a higher risk of heart attack, stroke or death than those diagnosed with viral pneumonia.

The results of the study were presented today (Nov. 11) at the American Heart Association’s annual Scientific Sessions meeting. The study has not yet been published in a peer-reviewed journal.

Both bacteria and viruses can cause pneumonia, and the infection is characterized by inflammation of the air sacs in the lungs.

For the study, researchers looked at data on about 4,800 patients diagnosed with pneumonia and hospitalized at a Utah hospital from 2007 to 2014. About 80 percent of the patients were diagnosed with bacterial pneumonia. The researchers then looked at data on these patients 90 days after diagnosis, noting which patients experienced a heart attack, stroke, heart failure or death. (The researchers followed the patients for 90 days because previous studies had shown that the risk of these complications increased 90 days after the pneumonia diagnosis.)

The researchers found that 34 percent of patients with bacterial pneumonia developed major cardiac complications within that 90-day window, compared to 26 percent of patients diagnosed with viral pneumonia.

So why might the bacterial version pose a greater threat to the heart? This difference is most likely because bacterial pneumonia causes more inflammation in the arteries – a risk factor for heart disease – than viral pneumonia, said senior author Dr. Joseph Brent Muhlestein, a cardiologist at Intermountain Heart Institute in Utah.

Bacteria and viruses infect the body in different ways, Muhlestein told Live Science. viruses enter cells and cause damage, while bacteria stay outside the cells and release toxins into the bloodstream. The latter mechanism leads to more inflammation. This latter mechanism causes more inflammation in the blood, which in turn causes damage to the lining of the arteries.

What’s more, bacterial pneumonia often causes higher fevers, higher levels of inflammatory markers in the blood and high white blood cell counts, Muhlestein says. (A high white blood cell count indicates that the body is battling an infection.) But even so, the symptoms of viral and bacterial pneumonia aren’t all that different – and most of the time doctors assume the infection is bacterial and start treating patients with antibiotics, he adds.

Muhlestein noted, however, that he was surprised by the findings. Previous studies have shown that people with underlying health conditions are much less likely to have a heart attack in the following year than those who didn’t get the flu vaccine.” So in the back of my mind, I was thinking, well, it could be that viral infections [like] the flu [are] a worse heart complication than bacterial infections – but that’s not what we found.”

In any case, “if you’re sick, you should go to the doctor,” he says. In fact, the study found that “people who got viral pneumonia still had heart complications – just not as many” with bacterial pneumonia.

Muhlestein says he also recommends that doctors prescribe antibiotics for patients who are old and have underlying health problems, even if they think the infection is a virus. That’s because these people have weaker immune systems, and it may be easy to develop a bacterial infection that can progress to pneumonia, he said.