Epidemiology of bacterial meningitis

Although meningitis is a notifiable disease in many countries, the exact incidence rate is unknown. Depending on age, geographic location, immune system function, and vaccine implementation, the incidence rates and causative organisms of bacterial meningitis differ greatly between different regions of the world.

In 2013, there were an estimated 303,500 deaths globally from meningitis, attributed to Streptococcus pneumoniae (n = 79,100), Neisseria meningitidis (n = 65,700), Haemophilus influenzae type b (Hib) (n = 64,400) and other agents (n = 94,200).  

The incidence of meningitis varies according to the specific etiologic agent, as well as in conjunction with a nation’s medical resources. The incidence is presumed to be higher in developing countries because of less access to preventive services, such as vaccination. In these countries, the incidence has been reported to be 10 times higher than that in developed countries. Bacterial meningitis occurs in about 3 people per 100,000 annually in Western countries. Population-wide studies have shown that viral meningitis is more common, at 10.9 per 100,000, and occurs more often in the summer. The annual incidence of bacterial meningitis in the United States is 1.33 cases per 100,000 population. 

Meningococcal meningitis is endemic in parts of Africa, India, and other developing areas. Periodic epidemics occur in the so­-called sub­Saharan “meningitis belt,” as well as among religious pilgrims traveling to Saudi Arabia for the Hajj. In parts of Africa, widespread epidemics of meningococcal meningitis occur regularly. In 1996, the biggest wave of meningococcal meningitis outbreaks ever recorded arose in West Africa. An estimated 250,000 cases and 25,000 deaths occurred in Niger, Nigeria, Burkina Faso, Chad, and Mali.

Demography of bacterial meningitis worldwide

The incidence of neonatal bacterial meningitis is 0.25­1 case per 1000 live births. In addition, the incidence is 0.15 case per 1000 full­-term births and 2.5 cases per 1000 premature births. Approximately 30% of newborns with clinical sepsis have associated bacterial meningitis.

N meningitidis causes approximately 4 cases per 100,000 children aged 1­-23 months. The risk of secondary meningitis is 1% for family contacts and 0.1% for daycare contacts. The rate of meningitis caused by S pneumoniae is 6.5 cases per 100,000 children aged 1­-23 months.

Previously, Hib, N meningitidis, and S pneumoniae accounted for more than 80% of cases of bacterial meningitis. Since the late 20th century, however, the epidemiology of bacterial meningitis has been substantially changed by multiple developments. The overall incidence of bacterial meningitis in the US declined from 2.0 to 1.38 cases per 100,000 population between 1998 and 2007. This was partially because of the widespread use of the Hib vaccination, which decreased the incidence of H influenzae meningitis by more than 90%. Routine Hib vaccination has nearly eliminating this pathogen as a cause of meningitis in many developed countries.

More recent prevention measures such as the pneumococcal conjugate vaccine and universal screening of pregnant women for GBS have further changed the epidemiology of bacterial meningitis.  Because the frequency of bacterial meningitis in children has declined, the condition is becoming more of a disease of adults. Whereas the median age for persons with bacterial meningitis was 25 years in 1998, it was 15 months in 1986. 

Deaths from meningitis per million persons in 2012 worldwide

Epidemiology of aseptic meningitis

Aseptic meningitis has a reported incidence of 10.9 cases per 100,000 person­-years. It occurs in individuals of all ages but is more common in children, especially during summer. No racial differences are reported. Aseptic meningitis tends to occur 3 times more frequently in males than in females.

Viruses are the major cause of aseptic meningitis. The enteroviruses are distributed worldwide, and the infection rates vary according to the season of the year and a population’s age and socioeconomic status. Most enteroviral infections occur in individuals who are younger than 15 years, with the highest attack rates in children who are younger than 1 year.

Arboviruses are an important cause of aseptic meningitis and encephalitis in the summer and fall months in the United States. West Nile virus was introduced to the United States in 1999 and has now spread throughout the continent. In 2012, the largest outbreak of West Nile virus infection to date occurred in the United States, with 5387 cases reported (about half of which were neuroinvasive disease, such as meningitis or encephalitis) and a 4.5% mortality. West Nile virus can also cause acute flaccid paralysis, retinitis and nephropathy.

Other less common arboviruses include St Louis encephalitis virus, Jamestown canyon virus, La Crosse encephalitis virus, Powassan encephalitis virus, and Eastern equine encephalitis virus. In the United States, the last epidemic of St Louis encephalitis was in Monroe, Louisiana, in 2001; 63 cases were reported, with 3 deaths (4.7% mortality). Infection with the La Crosse encephalitis virus also usually occurs during the summer and early fall, with symptoms again being typical of acute aseptic meningitis. 

Infections with the LCM virus occur worldwide. Most human cases occur among young adults during autumn.

Of fungal causes, B dermatitidis is reportedly endemic in North America (eg, Mississippi and Ohio River basins). It has also been isolated from parts of Central America, South America, the Middle East, and India. H capsulatum has been reported from many areas of the world, with the Mississippi and Ohio River valleys being the most endemic regions in North America.

Of parasitic causes, A cantonensis is common in Southeast Asia and the Pacific Islands. It has also been found in rats outside this region, particularly in regions of Africa, Puerto Rico, and Louisiana, presumably introduced by ship­borne rats from endemic areas. G spinigerum is common in Southeast Asia, China, and Japan but has been reported sporadically worldwide.

Epidemiology of chronic meningitis

Brucella ­associated chronic meningitis has a worldwide distribution and is common in the Middle East, India, Mexico, and Central and South America. In the United States, after the control of bovine infections, the incidence decreased to less than 0.5 cases per 100,000 population, and only 79 cases were reported to the CDC in 1998.

M tuberculosis is worldwide in distribution, and humans are its only reservoir. In 1997, the estimated case rates among endemic countries ranged from 62 to 411 cases per 100,000 population.

B burgdorferi is a tick­borne spirochete that is found in the temperate regions of much of the northern hemisphere. Endemic regions include North America (eg, the northeastern United States, Minnesota, Wisconsin, and parts of California and Oregon), Europe, and Asia.

C neoformans has a worldwide distribution. Serotypes B and C have been restricted mostly to tropical and subtropical regions, and serotype B has been isolated from eucalyptus trees.

The distribution of C immitis is limited to the endemic regions of the Western Hemisphere, within the north and south 40° latitudes (ie, parts of the southwestern United States, Mexico, and Central and South America). Persons who have migrated from or traveled to endemic areas may experience onset of disease in other parts of the world.

S schenckii has been reported worldwide. However, most cases come from the tropical regions of the Americas.