Outbreak of meningococcal disease in western Norway due to a new serogroup C variant of the ET-5 clone: effect of vaccination and selective carriage eradication

Abstract

A new sulphonamide resistant (SR) C: 15:P1.7,16 meningococcal strain, a variant of the ET-5 clone, dominated in an outbreak of 22 cases in western Norway commencing in 1995. The first eight patients were 15-21 years old from the Nordhordland area, initiating a carrier study in the local high schools. Carriage of SR serogroup C meningococci was detected by routine methods and treated with a single dose of ofloxacin 400 mg. Of 20 treated carriers, 14 harboured the outbreak strain C: 15:P1.7,16. Vaccination of 4000 children, adolescents and close contacts of patients was also performed. After the intervention, 14 additional cases of meningococcal disease occurred, 8 due to the outbreak strain. However, incidence rates dropped from 180 to 30 per 100000 per year in the student population, but increased from 0 to 13 in the rest of the population in Nordhordland. Carriage eradication is not generally recommended in Norway. However, tracing and treating meningococcal carriage may have reduced transmission and disease in this outbreak situation.

Use of Variable-Number Tandem Repeats To Examine Genetic Diversity of Neisseria meningitidis

“…Two of these isolates (N 100/96 and N 66/96) were from cousins and shared the same VNTR pattern, whereas the other two isolates (N 44/96 and N 109/96), which were from patients in different counties, had only 75% similarity to the first two. (33). All disease-associated isolates belonged to ET-5 and had the same phenotype, C:15:P1.7,16.…”

Predicting meningococcal disease outbreaks in structured populations

“…This same idea was apparently the motivation behind the old practice of culturing pharyngeal swab samples for the presence of meningococci from all members of the units in which meningitis had occurred. In many instances, the percentage of meningococcal carriers has been found to be high in the units in contact with cases, as compared to percentages in other units [8][9][10], but this has not always been so [11][12][13][14]. No apparent useful pattern has emerged from the crude carriage percentages [15,16].…”

“…No apparent useful pattern has emerged from the crude carriage percentages [15,16]. Instead, meningitis cases tend to occur within a few days after exposure, suggesting that the decisive factor is the acquisition of carriage [11,12,14,17]. Therefore, temporal observations on the number of carriers would contain useful information on the acquisition.…”

“…Figures from less than 20 per cent to over 70 per cent have been reported [14,18,19]. Improving the speciÿcity of the culture method to identify carriers of only the particular strain (deÿned by sulfonamide resistance or serotype, or more recently by serosubtype, or other clonal characteristic) that had caused the disease cases has given more relevant information [10,12,13,20], but still these data could not be directly applied for predicting the course of an outbreak. Unit speciÿc observations on carriers provide direct information on the development of the latent epidemic processes in the units.…”

Editorial Commentary: Epidemiology of Meningococcal Disease in Light of Recent Hajj‐Associated Outbreaks

“…Capsule switching can involve serogroups B, C, Y, and W135, the capsules of which are composed of polysialic acid or of sialic acid linked to glucose or galactose [12]. Capsule switching has been observed during outbreaks in the Czech Republic, in western Norway, in Oregon and Washington (in the United States), and in Spain [12][13][14][15]. Exchange of genetic material between strains can also result in changes in the outer membrane proteins that distinguish serotypes and subtypes [16].…”