MENINGOCOCCAL MENINGITIS OUTBREAK IN TRINIDAD, 1998

Aim: To describe an outbreak of serogroup B neisseria meningitidis occurred in Trinidad during 1998. Methods: Epidemiological survey was conducted following the identification of the fist case in El Socorroi Trinidat. Results: Thirteen other cases were detected with the majority found among the <5 age group which accounted for 42.9%, followed by the 45-64 age group with 14.3%. Mortality was 57.1%, highest among the <5 age group accounting for 50% followed by the 25-44 and 45-64 age groups with 25%, respectively. Two distinct clusters of N. meningitidis cases were identified using GPS/ GIS systems which graphically demonstrated the link between the two clusters. Conclusion: The implications of these results are discussed with respect to surveillance systems.


INTRODUCTION
The World Health Organization (WHO) estimates that 1.2 million cases of bacterial meningitis occur annually, with 135,000 deaths, making it a major cause of morbidity and mortality in both developed and developing nations.Neisseria meningitidis is the etiological agent in more than 40% of these cases (1).The African meningitis belt, which stretches from Senegal to Ethiopia, has the highest incidence of the disease, but N. meningitidis is also responsible for recent outbreaks in Asia and the Americas (2,3).Serogroup A has caused the majority of the African epidemics (4) while Serogroup C has caused outbreaks in North America as well as in Africa.However, serogroup B has caused sporadic outbreaks in South American and the Caribbean, including Cuba (1982)(1983)(1984), Chile (1986Chile ( , 1993)), Brazil (1988) and other parts of the world (4).
Meningitis is endemic in many countries in the Caribbean region, with causative agents varying from serogroup B Streptococcal meningitis in Trinidad and Cuba (5,6,7) to Hemophilus influenzae in Jamaica (8).In Trinidad, Streptococcal meningitis was found to be a very common clinical presentation (44%) whereas neonatal meningitis prevalence was found to be extremely low with 0.28% (49/17048) (5,6).
Trinidad and Tobago (population 1.2 million) generally has a low occurrence of meningococcal meningitis with only occasional isolated cases.
From 1990 to 1997 there was an average of 3 confirmed cases per year (Figure 1) but these cases were geographically isolated with no epidemiological clusters.During September-October 1998 a meningococcal outbreak occurred in Trinidad and this paper reports on the epidemiologic features of this outbreak of N. meningitidis serogroup B in Trinidad in 1998.

Background
The island of Trinidad is located approximately 11 0 North, 15 km from the east coast of Venezuela, from which it is separated only by the shallow Gulf of Paria (Map 1).The island is roughly rectangular in shape, with large promontories on the northwest and southwest and an area of circa 4662 km 2 .The island's greatest length is 90km, from north to south, and its greatest breadth is 57.6 km, from east to west.It has a population of about 1.2 million (9).
The case definition for confirmed cases was an isolate of N. meningitidis and consistent symptoms of meningitis including petechial rash in association with sudden onset of fever, headaches and stiff neck.The case definition for suspected cases was symptoms of headache, fever and stiff neck, with an absence of an isolate of N. meningitidis and no other obvious explanation for the observed symptoms.

Case Investigations
Following the identification of the first case of N. meningitidis a thorough investigation was conducted by a team of Epidemiologist, Medical Officers, Surveillance Nurses and District Health Visitors to determine the case distribution within the community including schools.From the end of September to December 1998 epidemiological studies were initiated including contact tracing, swabbing of the immediate family of all cases and neighboring household, and the provision of prophylactic treatment (Rifampicin) to all contacts and surveillance workers.
All positive isolates were sent to the Laboratory Centre for Disease Control (Federal Laboratories), Bureau of Microbiology, Winnipeg, Manitoba, Canada for serogroup typing.
During the outbreak, the location of every case was determined using a GPS (Trimble GeoExporer: Trimble Navigation, Sunnyvale and Garmin GP 45: Garmin International, Inc. Olathe, KS).Precise coordinates of all cases were entered into a GIS (ArcView, ESRI, Redlands, CA), and associated with attribute data of N. meningitidis.A spatial distribution map was produced using ArcView GIS.

RESULTS
On 1 st October 1998, a five year old boy who lived in Forress Park, Claxton Bay, was admitted to Port of Spain General Hospital and died within 24 hours of admission.A cerebral spinal fluid sample was sent to the Trinidad Public Health Laboratory and the Caribbean Epidemiology Centre for bacteriological testing.From the CSF sample Neisseria meningitidis serogroup B was isolated thus corroborating the diagnosis at post-mortem.Upon investigation, it was revealed that the child lived in close proximity to a sanitary landfill site in Claxton Bay (Map 1).Swabs taken from the mother of the child were found positive with N. meningitidis serogroup A, but she was asymptomatic suggesting a "carrier" status.
On further investigation an employee of a bakery in El Socorro, San Juan, Trinidad, died on 26 th September 1998.The owner of the bakery was found to be an asymptomatic "carrier" while his brother died 48 hours earlier falling victim to a similar infection and dying within 24 hours of admission to the St. Clair Medical Centre.Nasopharyngeal swabs were taken and demonstrated the presence of N. meningitidis serogroup B. The owner of the bakery is considered the index case but a "carrier".Twenty-one cases of suspected N. meningitidis were reported to the Trinidad Public Health Laboratory between 26 th September and 10 th December 1998.All cases were hospitalized.Fourteen cases were subsequently confirmed as N. meningitidis by bacterial culture.Figure 2 shows the sex and age distribution of the 14 confirmed cases, with the most significant age group contracting N. meningitidis being <5 with 42.9%, followed by the 45-64 age group with 28.6%.Overall, there was a 57.1% (8 cases) mortality rate among the 14 cases detected.The mortality rate was highest among the <5 year old with 50% (4 cases), followed by age groups 24-44 (2 cases) and 45-64 (2 cases) with 25% respectively.No deaths occurred among the other age groups.
The epidemiological curve or timeline indicated that over 38% of the cases were detected on the 17 th October 1998 (Fig. 3).Eleven cases were clustered from 3 rd October to 24 th October 1998 and had in common persons working, purchasing items or living in close proximity to the bakery in the town of El Socorro, Trinidad (See Map 1) An investigation on the linkage between the cases in El Socorro and the first case in Claxton Bay revealed that a garbage truck from opposite the bakery frequently transported materials to the dump at the Forress Park sanitary landfill in Claxton Bay.The other two cases, one of serogroup A and the other of serogroup B, were observed from other geographical locations and had no obvious factors linking them to the above cases.
The georeferenced database was used to calculate spatial distance between N. meningitidis cases and revealed two epidemiological clusters, one in El Socorro and the other in Forress Park, Claxton Bay, Trinidad (Map 1).

DISCUSSION
The small outbreak of N. meningitidis in Trinidad can be attributed to numerous factors, many of these factors are not fully understood, but a complex combination of host, agent and environmental risk factors appear to be involved.Results from Figure 1 showed that an average of 3 cases of meningitis is observed annually in Trinidad.These results suggest that N. meningitidis is endemic and maintained by "carriers" who made up over 28% of the cases identified during this outbreak.These results are consistent with carrier levels (25%) observed in the meningitis belt (10).
It has been reported that N. meningitidis serogroup B is commonly asymptomatic in the Americas and is not usually associated with clusters of cases but rather gives rise to sporadic cases (7,11)).However, the present outbreak was caused by serogroup B which suggests a possible change in pathogenicity or a recent introduction of a new pathogenic strain.
Some environmental factors such as low humidity, high temperature and dust have been suggested as factors for enhancing meningococcal invasion by directly damaging the mucosal barrier or by inhibiting mucosal immune defenses (12).The identification of four cases associated within a dusty sanitary landfill site supports the hypothesis that living, working and playing at such sites are risk factors.It is clear that although factors which predisposed a population to N. meningitidis are poorly understood, population susceptibility, introduction of new strains or "carriers", poor living environment, adults scavenging among contaminated materials at the dump, dusty environment and concurrent infections have been implicated (11,12,13, present study) The primary mode of transmission of the current outbreak was possibly by direct contact, including droplets and discharges from nose and throat of infected persons.Infection is likely to have occurred from contact with "carriers' identified during the outbreak investigation.The transmission to family, employees of the bakery and residents from the surrounding areas possibly occurred by contact with droplets while purchasing items or within the home.It is hypothesized that the infectious agent was transported from El Socorro to Forress Park via the garbage truck which dumped the potentially hazardous material at the landfill site (Map 1).
An important element of this meningitis

Figure 2 .
Figure 1.Annual number of Meningoccal cases observed in Trinidad during the period 1990-1997

Figure 3 .
Figure 3. Time-line of Neisseira meningitidis cases occurring during the months of September and October 1998