Ask the Doctors - How contagious is bacterial meningitis?

Dr. Robert Ashley, MD

Dear Doctor: One of the schools in my area has been the focus of news reports about a bacterial meningitis case. How contagious is this disease?

Dr. Robert Ashley
Dr. Robert Ashley

Bacterial meningitis cases in school-age children, adolescents and college students are predominately caused by two different organisms: Streptococcus pneumoniae and Neisseria meningitides. Streptococcous causes nearly 50 percent of meningitis between the ages of 2 and 18, while people in their teen and college years face an increased risk of meningitis caused by Neisseria meningitides. In fact, 45.9 percent of meningitis cases between ages 11-17 are due to N. meningitides.

The Streptococcus pneumoniae bacterium is spread by close contact with people who cough or sneeze the bacteria. Upon inhalation, the bacteria adhere to the back of the nasal passage in an area called the nasopharynx. Normally, there the bacteria sit, colonizing the nasopharynx without causing any problems. A study of 2,799 Italian children less than 7 years of age found that 8.6 percent had S. pneumoniae colonizing the nasopharynx; the biggest risk factor for colonization was a sinus infection over the last 3 months.

In most people with this colonization, the immune system keeps the bacteria from invading the cells of the body. However, when the immune system is weakened or when the body is fighting a viral infection, such as influenza, the bacteria can then invade the cells. From there, the bacteria can enter into the bloodstream and cross through the blood-brain barrier. When that happens, the bacteria replicate readily in the cerebrospinal fluid, leading to the symptoms of meningitis.

The Neisseria meningitides bacterium is passed from one person to the other by secretions from coughing or by saliva from kissing. It’s also passed easily among people in close contact. Like Streptococcus, Neisseria also settles in the nasopharynx, where the immune system similarly keeps the bacteria from invading into the cells of the body. People can carry the bacteria for several months within their nasopharynx and unwittingly pass it on to others. In fact, 5-10 percent of people in the United States carry this bacteria in the nasopharynx. Military recruits in closed quarters can have carrier rates up to 40 percent. College students in dormitory situations have carrier rates of 14-34 percent. If one person develops meningitis from N. meningitides, other people with whom they are in close contact are at greater risk.

Again, the bacteria that cause meningitis are quite contagious, but a person’s general risk of developing the illness is very low. In addition, children and adolescents are vaccinated for three types of bacteria that can lead to meningitis: Streptococcus pneumoniae, Neisseria meningitides and Haemophilus influenzae b. These vaccinations have significantly decreased the rates of meningitis, so make sure that your child gets these vaccinations. Lastly, if your child has been exposed to somebody with meningitis, watch for fever, neck stiffness and lethargy. If he or she begins to exhibit these symptoms, all potential signs of meningitis infection, take him or her to a doctor as soon as possible.

Robert Ashley, MD, is an internist and assistant professor of medicine at the University of California, Los Angeles.

Ask the Doctors is a syndicated column first published by UExpress syndicate.