Bacterial meningitis rates wane thanks to vaccines

Rates of deadly bacterial meningitis have dropped in the U.S. thanks to vaccination and prenatal screening, according to a study published in NEJM.

Rates of deadly bacterial meningitis have dropped in the United States thanks to vaccination and prenatal screening, according to a study published May 26, 2011, in the New England Journal of Medicine (NEJM). In 1998, there were two cases for every 100,000 people in the United States, but by 2007, that rate had dropped to 1.38 cases per 100,000 people. That may not seem like much, but for a population of 300 million people, it translates into a decrease from 6,000 cases to about 4,000 each year.

That decrease is important because bacterial meningitis can be a killer. In the NEJM study, led by Michael Thigpen of the Centers for Disease Control, the researchers evaluated data from all cases of bacterial meningitis reported for eight surveillance areas as part of the Emerging Infections Program Network. The network covered about 17.4 million people during the 1998 to 2007 study period. Among those millions, 3,188 people came down with some form of bacterial meningitis. Of the 3,155 cases for which the outcome was available, 14.8% died. That’s 466 people just in that surveillance area. Extending that country-wide, the investigators estimated that from 2003 to 2007, there were about 4,100 cases and 500 deaths each year from the disease.

Without vaccines against some of the primary culprits in bacterial meningitis and prenatal screening for group B streptococcus, which also causes it, the drop in cases would not have happened. As it stands, the increasing uptake of vaccinations has accompanied a stepwise decrease in bacterial meningitis infections, according to the researchers. The vaccines that prevent bacterial meningitis all target the primary bacterial agents of the disease and include conjugate pneumococcal vaccine, Hib (for Haemophilus influenzae type b), and conjugate meningococcal vaccines. Each of these contains molecular bits that trigger an immune memory of a disease without causing the disease itself. In this way, the body can mount a rapid and effective defense against a real invasion and prevent illness. The routine use of pneumococcal vaccines alone has reduced rates of that form of the disease by 59% in a decade.

Those agents that cause the disease are, of course, all bacteria. The one that infects most often is Streptococcus pneumoniae, which can cause infections in many tissues, including the lungs. As with the other infectious agents, when S. pneumoniae gets into the membranes that surround and protect the central nervous system, called the meninges, the result can be the deadly inflammation known as meningitis. The other most common causative agent is Neisseria meningitidis, which obviously gets its name from the disease that it causes.

In their analysis, the NEJM authors found that because of the younger age of the vaccinated group, the disease hit harder among older populations as the years passed. From 1998 to 1999, the midpoint age for the population stricken with the disease was 30.3 years. From 2006 to 2007, that midpoint had increased to almost 42 years. As the authors note, “the burden of bacterial meningitis is now borne by older adults.” It’s a change from when meningitis was best known as a sudden and dreaded killer of the young.

The bacteria that cause meningitis can be present in the nose or throat and often don’t cause any symptoms at all. But in the very young or old or those whose immune systems may be weakened, they can take deadly hold and debilitate or kill. The more common form of meningitis, viral meningitis, is a serious disease but not nearly as deadly the bacterial kind. Whether bacterial or viral, the symptoms of meningitis include a high fever and a headache and stiff neck. Sensitivity to light, lethargy, or vomiting may also be present. The disease, which can rapidly progress over only a few hours or take a couple of days to peak, can ultimately lead to seizures if it’s caused by a bacterial infection. For patients who survive the bacterial infection, the long-term outcomes can include neurological and auditory impairments and intellectual or behavioral disorders.

As Michael Thigpen and his co-authors report in their NEJM paper, preventive medicine such as vaccines and prenatal testing can reduce these kinds of outcomes by reducing bacterial meningitis infections themselves. This simple protection against devastating potential killers like Streptococcus pneumoniae and Neisseria meningitidis is just a shot away.

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