Meningococcemia epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Epidemiology and Demographics

• Case rate is 1-2 per 100,000 in the US in 1980. More recently, there are approximately 2,500 cases of meningococcal infections per year in the United States.
• Since the introduction of Haemophilus influenzae type b vaccine in 1990 for infants the majority of cases of bacterial meningitis have been in adults; historically 45-87% of cases have been in children.
• It occurs in both endemic and epidemic form
• Humans are the only natural reservoir of meningococcus. As many as 10% of adolescents and adults are asymptomatic transient carriers of N. meningitidis, most strains of which are not pathogenic (i.e., strains that are not categorized)
• Primary mode is by respiratory droplet spread or by direct contact.
• Meningococcal disease occurs throughout the year, However, the incidence is highest in the late winter and early spring.
• The communicability of N. meningitidis is generally limited. In studies of households in which a case of meningococcal disease has occurred, only 3%–4% of households had secondary cases. Most households had only one secondary case. Estimates of the risk of secondary transmission are generally 2–4 cases per 1,000 household members at risk. However, this risk is 500–800 times that in the general population.
• Second most common cause of community-acquired adult bacterial meningitis after pneumococcus.
• In West African countries during 1996-1997 there were 213,658 cases and 21,830 deaths due to menigococcal disease.
• Fewer than 1000 cases annually in the United States. Higher rates of disease occur in other countries. The largest burden is in sub-Saharan Africa, where epidemics during the dry season can cause disease in up to 2% of a population, resulting in thousands of cases and deaths during large epidemics.
• N. meningitidis may either be encapsulated or unencapsulated. However, nearly all invasive N. meningitidis organisms are encapsulated, or surrounded by a polysaccharide capsule. *This capsular polysaccharide is used to classify N. meningitidis into 12 serogroups.
• Six of these serogroups cause the great majority of infections in people: A, B, C, W135, X, and Y .
• Incidence rates of N. meningitidis are generally highest in children less than five years of age and in adolescents.
• N. meningitidis can also cause a severe bacteremia, called meningococcemia.
• The worldwide distribution of serogroups of N. meningitidis is variable.
• In the Americas, Europe, and Australia, serogroups B and C are the most common, while serogroup A causes the majority of disease in Africa and Asia .
• Sometimes serogroups can emerge, increasing in importance in a specific country or region, like serogroup C in China (20) or serogroup Y in North America.
• Worldwide, the incidence of meningitis due to N. meningitidis is highest in a region of sub-Saharan African known as the “meningitis belt” .
• This hyper-endemic region extends from Senegal to Ethiopia, and is characterized by seasonal epidemics during the dry season (incidence rate: 10-100 cases per 100,000 population), punctuated by explosive epidemics in 8-12 year cycles (incidence rates can be greater than 1,000 cases per 100,000 population).
• Across the meningitis belt, at least 350 million people are at risk for meningitis during these annual epidemics. Meningitis epidemics are generally caused by serogroup A, although outbreaks have also been caused by serogroups C, W135, and X.
• Outbreaks of different serogroups may overlap, therefore, laboratory confirmation is important both to recognize and monitor the progression of outbreaks.

[(http://www.cdc.gov/meningococcal/)]

Incidence

• Prior to 2000, an estimated 1,400 to 2,800 cases of meningococcal disease occurred each year in the United States, a rate of 0.5 to 1.1 per 100,000 population.
• The proportion of meningococcal cases caused by serogroup Y increased from 2% during 1989 through 1991 to 37% during 1997 through 2002.
• Serogroups B, C, and Y are the major causes of meningococcal disease in the United States, each being responsible for approximately one third of cases.
• Among infants younger than 1 year of age, more than 50% of cases are caused by serogroup B, for which no vaccine is licensed or available in the United States.
• Of all cases of meningococcal disease among persons 11 years of age or older, 75% are caused by serogroups C, Y, or W-135.
• Meningococcal disease incidence has decreased since 2000, and incidence of serogroups C and Y, which represent the majority of cases of vaccine-preventable meningococcal disease, are at historic lows.
• A peak in disease incidence among persons 18 to 21 years of age has persisted, even after routine vaccination of adolescents was recommended in 2005.
• From 2000–2004 to 2005–2009, the estimated annual number of cases of serogroups C and Y meningococcal disease decreased 74% among persons aged 11 through 14 years but only 27% among persons aged 15 through 18 years.

[(http://www.cdc.gov/meningococcal/)]

National meningococcal disease estimate

Race	Number	Rate
White	42	0.13
Black	16	0.21
Other	4	0.12
Total	62	0.14

Syndrome	Cases	Death
Meningitis	31	4
Bacteremia without focus	13	3

Cases per 100,000 population of various serotypes

Age	Serogroup B	Serogroup C	Serogroup Y	Serogroup Other
<1	0.62	0.00	0.00	0.21
1	0.21	0.41	0.00	0.00
2-4	0.07	0	0	0.20
5-17	0.02	0	0	0
18-34	0.04	0.05	0.03	0.04
35-49	0.04	0.08	0.03	0.01
50-64	0.04	0.00	0.03	0.01
>=65	0.02	0.06	0.02	0.02
Total	0.04	0.04	0.02	0.03

Age

Most cases of meningococcemia occur in children, but other age groups may be involved as well.

[(http://www.cdc.gov/meningococcal/)]

The following are statistics regarding college aged students:

• Rates of meningococcus in US college students as a whole 0.7 per 100,000.
• Rates of meningococcus in US persons aged 18-23 not in college 1.5 per 100,000.
• Rates of freshmen living in dormitories 4.6 per 100,000.
• Rates for college students in UK 13.2 per 100,000 versus those not in college of 5.5 per 100,000.