Pneumonia can rapidly become serious, particularly for seniors, so get treatment early.

Pneumonia is sneaky. Although people with pneumonia occasionally have the classic signs—fever, flushed cheeks, rattling lungs, and discolored (green-brown) mucus—pneumonia is more likely to produce symptoms common to scores of other maladies. Because it often evades detection, pneumonia has been a leading cause of death in the United States for more than a century. “Pneumonia in all ages is really hard to diagnose because the symptoms aren’t specific, and older people are less likely to have typical symptoms than younger ones,” says Dr. Sophia Koo, assistant professor of medicine at Harvard Medical School.

What causes pneumonia?

Pneumonia is an inflammation of the lungs. The vast majority of cases are due to airborne microbes, usually bacteria or viruses. The most common cause of bacterial pneumonia is Streptococcus pneumoniae, or pneumococcus. Your susceptibility to pneumonia depends on three things:

• How healthy you are. Unlike upper respiratory viruses, which set up housekeeping in your nose and throat, pneumonia-causing pathogens have to evade the immune system and travel into your lungs. It’s much easier for them to sneak by when your immune system is exhausted from trying to fend off another infection or is compromised by a chronic disease. That’s why a bout of the flu or other viral infection can set the stage for pneumonia.

• Your age. Your immune response tends to be less robust as you get older. If you’re over 65 it’s important to be vaccinated against pneumococcus, and to get your yearly flu shot.

• Your environment. If there are colds going around or a flu epidemic in your area, your risk of pneumonia rises. Pneumonia risk is also elevated for people who are hospitalized, because they are likely to have depressed immune systems and are exposed to more germs.

Pneumonia symptoms

The body’s inflammatory response is responsible for the symptoms of pneumonia. When pneumonia is caused by a virus, the symptoms are likely to resemble those of the flu: fever, muscle aches, dry cough, and fatigue. The symptoms of bacterial pneumonia are usually more dramatic: fever with cycles of chills, body aches, and wracking coughs that produce rusty or yellow mucus. It hurts to inhale, and breathing causes sounds called rales and crackles.

However, if you’re older and have a less robust immune response, symptoms may be more vague. You are less likely to run high fevers or cough up a lot of mucus. Instead, you may feel confused, fatigued, or just not quite right.

If you have any symptoms, even low-grade symptoms, it’s important to be checked out by a doctor. The longer you wait, the more difficult your pneumonia may be to treat. “Pneumonia is a leading cause of death, so it’s important to get examined. No one is going to fault you for coming in, even for just feeling under the weather,” Dr. Koo says.

Pneumonia treatment

Viral pneumonia usually gets better without treatment. During a flu epidemic, when it’s likely that pneumonia is due to the flu virus, oseltamivir (Tamiflu), a drug developed to treat influenza infections, may relieve symptoms.

Bacterial pneumonia is treated with antibiotics. Which antibiotics are used depends on the type of bacteria responsible, and that in turn depends on where you caught pneumonia. Mild cases of pneumonia may be treated with oral antibiotics at home. More severe cases require hospitalization and intravenous antibiotics.