Hillary Clinton’s physician, Dr. Lisa Bardack, on Wednesday released a statement describing the Democratic nominee’s illness as a “mild non-contagious bacterial pneumonia,” adding a CT scan had revealed a small right middle-lobe pneumonia.

Bardack’s diagnosis led skeptics to question whether Clinton was, in fact, not contagious. Dr. Milton Wolf, a diagnostic radiologist running for the U.S. Senate in Kansas, tweeted “There’s no such thing as ‘non-contagious bacterial pneumonia.’ That’s pure fiction. Find a medical textbook with it.”

Wolf is technically correct: “‘non-contagious bacterial pneumonia" is not used in medical terminology. But there are bacterial pneumonias that are essentially non-contagious, experts who spoke with FoxNews.com said.

“When we talk about pneumonia, we don’t necessarily talk about whether it’s communicable or not unless it’s one of the diseases of great public interest, such as influenza, Legionnaire’s disease, and tuberculosis,” Dr. Richard Wunderink, professor of pulmonary and critical care at Northwestern Medicine, told FoxNews.com. “It’s very important to report tuberculosis, but we don’t even report if you have, say, pneumococcal pneumonia, the most common bacterial pneumonia, or mycoplasma pneumonia, another common bacterial pneumonia.”

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Wolf’s comment is “way too simplistic,” said Wunderink, adding there’s a debate in the scientific community over whether bacterial pneumonia is communicable. Unlike viral pneumonia, which has a clear correlation— for example, a sick child comes home with a virus, and soon the parents have the illness as well— that doesn’t happen so much with bacterial pneumonia.

“You don’t see whole families getting pneumonia,” said Wunderink. “There is an increased risk, but it’s not as dramatic as it is with viral [infections].”

With bacterial pneumonia, there is a significantly lower risk that superficial contact will spread. And even in a case of close physical contact, a bug that spreads to another person’s respiratory tract doesn’t necessarily mean it will develop into pneumonia.

Examples of non-contagious bacterial pneumonia include aspiration pneumonia, pneumonia following a procedure such as surgery within and around the lungs, and post-viral bacterial pneumonia, a secondary infection following influenza, according to Dr. Frank Esper, assistant professor in pediatric infectious diseases at Rainbow Babies and Children’s Hospital in Cleveland.

There is no test of whether a pneumonia patient is contagious. And pneumonia patients treated on an outpatient basis are typically not tested to determine the exact bacteria that caused their illness.

In fact, a study published last year by Wunderink’s team, in collaboration with the Centers for Disease Control and Prevention in the New England Journal of Medicine, found that with a very aggressive diagnostic approach, researchers could not find the cause of 64 percent of patients’ illnesses.