Bacterial meningitis has been classified into the category IV infectious diseases to be reported by sentinels in compliance with the April 1999 enactment of the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law). Approximately 500 sentinel hospitals make weekly reports of bacterial meningitis patients diagnosed on the basis of clinical symptoms and on the tests of cerebrospinal fluid, or etiological/serological diagnosis by sex and age (the etiological agent, if identified, is also reported). Most bacterial meningitis cases found within Japan are sporadic ones.

Epidemics of meningococcal meningitis occur in that part of sub-Saharan Africa known as the "meningitis belt" (see WHO, WER, 76, No. 37, 2001), and the case-fatality rate of meningococcal meningitis once affected is high. Since grasp of the index case including an imported one is urgent for preventing spread of this infection, the disease was included in the category IV infectious diseases to be notified by all physicians. The physician must report the meningococcal meningitis case within 7 days of confirmatory etiological diagnosis.

The following is a summary of the results of the national surveillance programs and of the surveys conducted by research groups:

The National Epidemiological Surveillance of Infectious Diseases (NESID): Bacterial meningitis cases reported during April 1999 and December 2001 totaled at 763 (235 during April-December 1999, 256 in 2000 and 272 in 2001). Those aged 0 and 1-4 years are both accounted for 29% and the ratio of male versus female cases was 456:307. More male cases were shown in any age group (Fig. 1). The etiological agents were recorded in about half of the cases; 143 cases were ascribed to Haemophilus influenzae and 90 to Streptococcus pneumoniae , followed by 22 to group B Streptococcus (GBS), and 14 to Escherichia coli . Less than 10 cases were ascribed to each of the other agents.

Meningococcal meningitis cases diagnosed during this period numbered at 33 (10 during April-December 1999, 15 in 2000 and 8 in 2001). Their ages ranged from 0 to 71 years; 6 cases each were 0 year, 1-14 years, and 15-19 years, and 15 cases of adults. Male cases numbered 28 and female ones numbered 5 (Fig. 2).

Infectious agent surveillance: Of all 96 etiological agents that were isolated from meningitis patients during 1995-2001, 28 each were H. influenzae and S. pneumoniae according to the case reports that were sent from the cooperating general clinical institutions to the Infectious Disease Surveillance Center (IDSC), the National Institute of Infectious Diseases (NIID) through the prefectural and municipal public health institutes (PHIs) (see p. 38 of this issue). H. influenzae was isolated mostly from children under 4 years of age, while S. pneumoniae from both children and those aged over 30 years. Such a tendency is similar to that of 1990-1994 (see IASR, Vol. 16, No. 4, 1995).

Isolation of pathogenic bacteria from cerebrospinal fluid: The Japanese Nosocomial Infection Surveillance (JANIS) of the Ministry of Health, Labour and Welfare (MHLW) has been enrolled since April 2000 (http://idsc.nih.go.jp/index-j.html). In the data of October -December 2000, 356 strains of pathogenic bacteria were isolated from cerebrospinal fluid at laboratories of approximately 500 cooperating medical institutions (with more than 200 beds each). The notable bacterial species were Staphylococcus aureus (17%), Staphylococcus epidermidis (15%), Coagulase-negative Staphylococcus (CNS: 10%), H. influenzae (11%), and S. pneumoniae (7%) (Fig. 3).

Surveys for pediatric bacterial meningitis cases in Japan: According to the three surveys conducted by H. Kamiya and his associates during 1994-1998, 60-70% of the etiological agents of bacterial meningitis among children under 5 years of age were H. influenzae , followed by S. pneumoniae . Neisseria meningitidis was very rarely involved. Meningitis caused by H. influenzae stood at a rate of 9-10 per 100,000 children aged under 5 years, accounting for about 600 cases per year (Antibiotics and Chemotherapy, Vol. 16, No. 11, 75-81, 2000).

According to the survey conducted by K. Sunakawa and his associates, among the pathogenic agents of bacterial meningitis during July 1997 through June 2000, H. influenzae was most prevalent, followed by S. pneumoniae , GBS, and E. coli , in this order (Table 1). Among the age distribution of the patients yielding the most prevalent bacterial species (Fig. 4), those yielding GBS were mainly infants under 4 months of age, and those yielding E. coli were all infants under 2 months of age. Those yielding H. influenzae were principally at ages of 3 months to 4 years, particularly younger than one year. Those yielding S. pneumoniae except for one strain were at ages of 2 months-10 years. More patients at the ages of 5 years and older were involved (see p. 33 of this issue).

N. meningitidis -carrying rate of healthy population: Although nine patients were reported during April 1998 through October 1999 in Tokyo (see IASR, Vol. 21, No. 3), there have been very few reports of meningococcal meningitis in Japan. To clarify the background of this, a study group on case finding and laboratory confirmation of meningococcal meningitis (headed by S. Yamai, Kanagawa Prefectural Public Health Laboratory) of the MHLW conducted a survey in the year 2000 in cooperation with six PHIs. They found healthy individuals carrying N. meningitidis (college students, etc.) with a rate of as low as 0.3% (five among 1,711 individuals). The isolates were neither of group A nor C, which are regarded as highly pathogenic, but of exclusively groups B and Y (see p. 37 of this issue).

Immunization against bacterial meningitis: In overseas, prevention and control of bacterial meningitis is in progress by developing and introducing vaccines against H. influenzae , S. pneumoniae and N. meningitidis . In USA, H. influenzae type b (Hib) conjugate vaccine was introduced in 1988 for infants at ages of 18 months to 5 years. Nevertheless, the routine vaccination was started in 1990. During 1989-1995, Hib infection of children at ages under 5 years decreased by 95% (see CDC, MMWR, Vol. 47, Nos. 35 & 46, 1998). At present, as a recommended immunization schedule, Hib vaccine is administered at ages of 2, 4, 6, and 12-15 months (see CDC, MMWR, Vol. 51, No. 2, 2002). In Canada, 23-valent pneumococcal polysaccharide vaccines were previously recommended for use in children over 2 years of age. A newly licensed heptavalent pneumococcal conjugate vaccine is recommended for use in children under 2 years of age (at 2, 4, 6, and 12 to 15 months of age) (see Canada CCDR Vol. 28, ACS-2, 2002). In UK, infants under one year of age and teenagers of 15 to 17 years were the first target of group C conjugate meningococcal vaccine introduced in November 1999 and all children under 18 years of age were vaccinated by autumn of 2000. In the year 2002, vaccination of those aged under 24 years has been recommended (see CDSC, CDR, Vol. 10, No. 15, 2000 and Vol. 12, No. 2, 2002). Outbreaks of group W135 meningococcal infection occurred among pilgrims returning from Mecca in many countries in 2000 and 2001 (see CDC, MMWR, Vol. 49, No. 16, 2000; CDSC, CDR, 11, Nos. 2&19, 2001). The Department of Health of UK recommended immunization with quadrivalent meningococcal vaccine (A, C, W135, and Y) for pilgrims to Mecca in 2002 (see CDSC, CDR, Vol. 12, No. 3, 2002).

Future problems: Since increase of drug-resistant organisms of H. influenzae and S. pneumoniae , the main pathogenic agents of bacterial meningitis in Japan, have been reported (see p. 34-36 of this issue), rapid diagnosis of the etiological agent and selection of adequate chemotherapy are required at the therapy site. It is needed to further intensify the pathogenic agent surveillance, monitoring species and type of meningitis etiological agents and their drug susceptibilities and promoting countermeasures against drug-resistant organisms and introduction of vaccines.