President George H.W. Bush: What can cause a persistent fever?

Former President George H.W. Bush was admitted to the intensive care unit of a Houston hospital Sunday, a spokesman announced Wednesday. There aren’t a lot of details, but the former president, who is 88, originally went to Methodist Hospital on Nov. 23 with a lingering cough. That improved, but he remained in the hospital over Christmas and was admitted to the ICU after setbacks that included a persistent and rising fever.

We spoke with Dr. Kent Shoji, emergency room physician at Marina Del Rey Hospital in Marina del Rey — who isn’t involved in the former president’s care — about the various causes of lingering fevers.

“The majority of times that you get a fever it indicates an infection,” Shoji said. But, he added, there are many other possible causes.

Persistent fevers can, for example, be caused by reaction to a medication to which a patient, unbeknownst to a doctor, is allergic. Or, rarely, a patient could be suffering from an autoimmune condition such as lupus, rheumatoid arthritis or gout. Sometimes, patients can be in a hypermetabolic state due to an overactive thyroid gland, Shoji said: “People come in with a heart rate of 150, really, really hyper and a fever of 101 or 102.”

Cancers, too, can sometimes be the cause of a persistent fever. “Cancer is a hypermetabolic state,” Shoji said. “The cancer cells are more metabolically active, they are duplicating and spreading and can cause a low grade fever.”

Because infections — viral, bacterial, fungal or parasitic — are the most common cause, doctors want to try to rule that out and start treating them, especially in higher risk patients such as the elderly and very young. (Infections can move fast and threaten life in susceptible people.)

Among individuals in their 70s and 80s, lung infections are common; in men, so are prostate infections, and in women, urinary tract infections. Infections of the gastrointestinal tract or blood are other possibilities. People who are older often have other medical conditions — so-called comorbidities — that put them at higher risk. They also have weakened immune systems and thus can’t fight off infections as rapidly as younger people.

Chest X-rays, blood counts and urine analysis help sort out the cause when a patient arrives at the ER with an elevated temperature. The blood is tested for its level of lactic acid; if it is high, that could mean that anaerobic (oxygen-free) metabolism is taking place in the body and would suggest a bacterial infection. Very high lactic acid levels indicate possible sepsis, a reaction of the body to a systemic infection.

In case of suspected infections, those who are at higher risk because of age or other medical conditions are admitted and started on antibiotics because they are at heightened risk. But an otherwise healthy man of 25 might be given a prescription for antibiotics and sent home, Shoji said.

If ones hears that a patient has been admitted to the ICU, Shoji said, “then you start worrying about pneumonia.” Anyone with reduced lung impairment due to past smoking habits or occupational exposure to lung-damaging toxins would be at heightened risk because these cause the lungs to be a bit weaker, he said. And, he added, “Pneumonia is very common in older people and sometimes even strong antibiotics don’t help” because of immune impairments.