Recent Increase in Meningitis Caused by Neisseria meningitidis Serogroups A and W135, Yaounde, Cameroon

Marie-Christine Fonkoua, Muhamed-Kheir Taha, Pierre Nicolas, Patrick Cunin, Jean-Michel Alonso, Raymond Bercion, Jeanne Musi, and Paul M.V. Martin

Emerging Infectious Diseases. 2002;8(3) 

In This Article

Abstract and Introduction

From 1991 to 1998, Neisseria meningitidis serogroups A, B, and C represented 2%-10% of strains isolated from cases of bacterial meningitis in Yaoundé. During 1999 to 2000, the percentage of meningococci reached 17%, a proportion never reported since recordkeeping began in 1984. The increase of serogroup A meningococci and the emergence of W135 strains highlight the need for increased surveillance for better diagnosis and prevention.

Neisseria meningitidis serogroup A causes major epidemics of meningitis in Africa, essentially within the African meningitis belt[1]. Epidemics of cerebrospinal meningitis in this belt are often enormous[1]. During the first 9 months of 1996 in the World Health Organization (WHO) African Region, 146,166 cases were reported to WHO; 15,783 were fatal. During that year, 42,129 cases occurred in Burkina Faso, 7,244 in Mali, 16,050 in Niger, and 75,069 in Nigeria. These four countries reported 95% of the cases in Africa in 1996, for an overall case-fatality rate of 10.6%[2].

The recommended control practices in Africa involve vaccination with the meningococcal bivalent polysaccharide A/C vaccine in response to epidemics. Efficient public health practice necessitates that epidemics be detected early, stocks of vaccines be set up in target regions, and field vaccination with the bivalent vaccine be rapid, since the quadrivalent ACYW135 vaccine has limited worldwide supply and is more expensive.

The presence of N. meningitidis serogroup W135 has been confirmed in Africa for some time. In Burkina Faso in 1980, 1.3% of the meningococcal strains isolated from rhinopharyngeal carriers belonged to serogroup W135. In 1981 and 1982, monitoring of the serogroups responsible for meningococcal meningitis at Dakar (Senegal) and Niamey (Niger) showed that 4% and 3% of strains, respectively, belonged to serogroup W135[3]. In 1984 and 1985, 7% of N. meningitidis strains isolated from meningitis cases in Gambia belonged to serogroup W135[4]. In 1993 and 1994, two strains of N. meningitidis W135 were isolated from patients in Mali; both belonged to the ET-37 complex[5]. More recently, in 1994, six strains of serogroup W135 isolated from clinical cases in Gambia were studied; they also belonged to the ET-37 complex. DNA macrorestriction analysis of these strains identified four different profiles in pulsed-field gel electrophoresis (PFGE), indicating that the strains involved were closely related but different[6]. W135 strains are often isolated after intensive campaigns of vaccination against meningococci of serogroups A and C[3,4,6].

In spring 2000, an epidemic of N. meningitidis W135 infection broke out among Hajj pilgrims (for whom vaccination against meningococci of serogroups A and C is mandatory) and their close contacts. In all, 241 cases were reported in Saudi Arabia and 90 in 13 other countries[7], including the United States (4 cases)[8], the United Kingdom (33 cases), and France (19 cases). All these strains showed markers of the ET-37 complex; had an antigenic formula W135:2a:P1-5,2; a sequence type ST-11; and the same profile on PFGE[9], confirming the clonal origin of the epidemic. Four W135 strains isolated in U.S. patients epidemiologically linked to Hajj pilgrims were further studied. The sequence of the porA gene showed that these four strains had variable regions VR1 and VR2 identical to those of the prototype P1.5,2 strain[8].

Apparently, the W135 strains isolated in Africa until 1995 did not cause large epidemics, even if isolated in the countries in the African meningitis belt in which epidemics due to serogroups A meningococci are frequent (e.g., Niger, Mali, Senegal, and Gambia). In Niger in 1981, only one W135 strain of 231 meningococci was isolated from a meningitis case[3]. Similarly, W135 accounted for 7 of 42 strains in 1982 in Niger, and 3 of 76 strains in Senegal in 1981 to 1982[3], 3 of 41 in Guinea in 1984 to 1985[4], and 2 of 75 strains isolated in 1991 to 1994 in six countries in the African meningitis belt[5]. However, available information shows that the case-fatality rate due to W135 strains was relatively high in Africa before 1995, as in Europe during the recent Hajj 2000 epidemic: 6 (35%) of 17 cases in Africa before 1995 (in Senegal, Gambia, and Niger) and 10 (18%) of 56 cases in Europe in 2000 (in the United Kingdom, France, and the Netherlands).