Absence of Neisseria meningitidis W-135 Electrophoretic Type 37 during the Hajj, 2002

We document the absence of carriage of Neisseria meningitidis W-135 of the sequence type 11 in returning pilgrims after the Hajj 2002. This finding contrasts with the 15% carriage rate we previously reported in pilgrims returning from the Hajj 2001. The epidemiology of carriage may be changing or may have been controlled by vaccination and a policy of administering antibiotics to pilgrims from countries with a high incidence of meningococcal disease.

We document the absence of carriage of Neisseria meningitidis W-135 of the sequence type 11 in returning pilgrims after the Hajj 2002. This finding contrasts with the 15% carriage rate we previously reported in pilgrims returning from the Hajj 2001. The epidemiology of carriage may be changing or may have been controlled by vaccination and a policy of administering antibiotics to pilgrims from countries with a high incidence of meningococcal disease.
T wo million pilgrims from all over the world congregate for the annual Islamic pilgrimage to Mecca and Medina in Saudi Arabia (Hajj pilgrimage). Because overcrowding facilitates person-to-person transmission of meningococci, this pilgrimage has been associated with meningococcal disease outbreaks (1)(2)(3). An international outbreak of serogroup W-135 meningococcal disease occurred during the Hajj pilgrimages in 2000 and 2001 (4,5). The outbreak-associated W-135 strains were of a single clone of the electrophoretic type (ET)-37 complex (6) and were closely related to other meningococci with an established propensity to cause disease clusters (7). Several reports from all over the world have shown that this W-135 outbreak strain affected not only pilgrims but also household contacts of returning pilgrims and the community at large, with the potential of non-Hajj-related further epidemics (8)(9)(10)(11)(12). As nasopharyngeal carriage is the primary source of transmission (13), worldwide dissemination is thought to be due to pilgrims who acquired W-135 carriage during the pilgrimage and introduced the strain on return to their countries of origin (14). We previously reported a 15% carriage rate of Neisseria meningitidis W-135 in Singaporean pilgrims returning from the Hajj 2001, despite the fact that all were vaccinated with quadrivalent polysaccharide meningococcal vaccine (15). W-135 carriage was substantially transmitted to unvacci-nated household contacts (15,16). Pulsed-field gel electrophoresis (PFGE) of these isolates showed that they were distinguishable in 83% of the samples (unpub. data), indicating that this outbreak had a clonal origin. The high transmission rate of W-135 carriage from pilgrims to household contacts translated into a high attack rate of W-135 meningococcal disease among contacts in 2001 (17). We investigated carriage rates in pilgrims returning from the 2002 Hajj to determine whether W-135 was still a problem, and we compared the strains from 2002 with those from 2001 to document the evolving molecular epidemiology of Hajj-associated W-135 strains.

The Study
We conducted a prospective study on the acquisition of meningococcal carriage in Singaporean Hajj pilgrims on the Hajj 2002. We used the same design and methods as we used in our previous study for the Hajj 2001, and the study was performed by the same research and laboratory staff (15). Pilgrims were recruited consecutively at the time of vaccination with quadrivalent meningococcal and influenza vaccine at a Muslim center that performs mass vaccinations for pilgrims referred by numerous national Muslim travel agencies. A swab sample was taken from both tonsils and the pharyngeal wall, by using a standard technique, and immediately transferred to a plate of selective culture medium (Oxoid GC, Basingstoke, UK). Repeat swab samples were taken 2 weeks after return from the pilgrimage. Returning pilgrims were asked if the symptoms of upper respiratory tract infection had occurred and if antibiotic drugs were taken during the pilgrimage, specifically a single dose of ciprofloxacin. All study participants gave written informed consent. The study was approved by the Ethics Committee of Tan Tock Seng Hospital.
Culture plates were immediately put in candle jars, transferred to the laboratory within 2 to 4 hours of collection, incubated at 37°C in humidified air with 5% carbon dioxide, and examined for bacterial growth at 24 and 48 hours (18). Identification of isolates as N. meningitidis was performed by traditional methods and was confirmed by API NH (BioMerieux SA, Lyon, France). The serogroup was determined by slide agglutination with polyvalent sera and serogroup-specific sera (A, B, C, D, Y, W-135, X, and Z) (Murex, Dartford, UK).
PFGE was performed on all meningococcal isolates by using previously described methods (19). The restriction enzyme used was SpeI. Multilocus sequence typing (MLST) was performed on all W-135 isolates, as well as on stored isolates from the 2001 Hajj, as described by Maiden et al. (20) by sequencing of seven housekeeping genes. Primers, determination of sequence alleles, and designation of sequence types are described on the MLST Web site (available from: URL: http://neisseria.org/ nm/typing/mlst). Participant demographics, duration of stay at the Hajj, respiratory symptoms, antibiotic intake, carriage rates, and results of PFGE and MLST were compared with the findings by our group from Singaporean pilgrims returning from the Hajj 2001 (15).

Conclusions
Tonsillopharyngeal swab samples were taken from 193 Malay pilgrims at a median time of 30 days (range 18-52) before their departure for the Hajj. One hundred fiftythree (79%) had a repeat swab sample taken at a median time of 10 days (range 2-17) after their return from the Hajj. The mean age was 48 (SD 8.07) years, and 48% were male. The mean duration of stay was 33 days (range 14-41, SD 3.6). Returning pilgrims reported cough (70%) and use of antibiotics (52.9%). Nine percent of pilgrims reported ciprofloxacin use.
Four of the pilgrims (2.6%) were carriers before the Hajj. Three isolates could not be grouped; one was serogroup B. Two (1.3%) of the returning pilgrims were carriers, and both isolates were serogroup W-135. The  (21). Therefore, in 2002, the W-135 carriage was probably also low in pilgrim populations other than these from Singapore.
The marked difference in W-135 carriage rates is unlikely to be due to selection bias or study methods, as we   (9), whereas almost complete vaccine coverage for this pilgrimage can be assumed for the year 2002 after this vaccine became a Hajj visa requirement for all pilgrims (21). Although polysaccharide vaccine does not prevent acquisition of carriage (13), as confirmed in our 2001 cohort (15), polysaccharide vaccines can induce transient reduction of carriage (24). In addition, vaccines reduce the incidence of meningococcal disease and thus circulation of meningococci. Almost complete vaccine coverage of 2 million pilgrims may have therefore contributed to a decrease in the spread of carriage within this pilgrim population and consequently reduced transmission of carriage from returning pilgrims to their contacts.
The significant decrease of W-135 meningococcal carriage and the absence of ST-11 in returning pilgrims from the Hajj 2002 are important findings with regard to public health policy. Our documented low W-135 carriage rate in Singaporean pilgrims in the year 2002 is indicative of a decreased potential for spread of meningococcal disease in close contacts of returning pilgrims. On the basis of the high carriage rate in returning pilgrims, together with the transmission to household contacts and observed secondary cases in the community in 2001 (16,17), we suggested that administrating antibiotics to returning pilgrims would be appropriate (15). Indeed, the Saudi Arabia authorities have implemented such a policy for their returning Saudi pilgrims (23). However, the epidemiologic features of carriage may be changing or has been controlled by vaccination and administering antibiotic drugs to incoming pilgrims from countries with high incidence. Thus, the administration of antibiotics to all returning pilgrims appears to be unnecessary at the present time. Ongoing surveillance of carriage rates both in the resident population in Saudi Arabia as well as in arriving and departing pilgrims is paramount for rapid readjustment of a policy to administer antibiotics to eradicate carriage.