Australian Meningococcal Surveillance Programme Annual Report, 2023.

In Australia, both probable and laboratory-confirmed cases of invasive meningococcal disease (IMD) are reported to the National Notifiable Diseases Surveillance System (NNDSS). When compared to 2022, the number of IMD notifications in 2023 increased by 14% to 143. Laboratory confirmation of IMD occurred in 140/143 (98%) of these cases, with 64% (90/140) diagnosed by bacterial culture and 36% (50/140) by nucleic acid amplification testing. The serogroup was determined for 96% of laboratory-confirmed cases (134/140): serogroup B (MenB) accounted for 84% of infections (112/134); MenW for 8% (11/134); MenY for 8% (11/134). There were no infections attributed to MenC disease. Fine typing was available on 75% of the cases for which the serogroup was determined (100/134). In MenB isolates, 25 types were detected, the most prevalent of which were P1.7-2,4 (32%; 26/82), P1.7,16-26 (16%; 13/82) and P1.22,14 (9%; 7/82). All eight typed MenW infections identified as type P1.5,2, with two different multi-locus sequence types (MLST) present: ST-11 (5) and ST-1287 (3) from the clonal complex 11, the hypervirulent strain reported in outbreaks in Australia and overseas. In MenY, the predominant type was P1.5-1,10-1 (90%; 9/10), ST-1655 and from clonal complex 23. Peaks of IMD occurred in children aged less than 5 years and in those aged 15-24 years, accounting for 21% (30/140) and 26% (37/140) of laboratory-confirmed cases respectively. In children aged under 5 years, 93% of IMD (27/29) was MenB; in those aged 15-24 years, 97% of IMD (36/37) was MenB, with serogroup not determined for one case in each of these age groups. Of note, 14-15% of IMD occurred in each of the older age groups reported: adults 25-44 years (14%, 19/140), 45-64 years (14%, 20/140), and in those aged 65 years and older (15%, 21/140). Whilst MenB predominated in all age groups, the majority of MenY and MenW IMD cases were reported in adults aged 45 years and older. All cultured IMD isolates (n = 90) had antimicrobial susceptibility testing performed. Minimum inhibitory concentration (MIC) values were reported using Clinical Laboratory Standards Institute (CLSI) interpretative criteria: 9% (8/90) were defined as penicillin resistant (MIC value: ≥ 0.5 mg/L); 71% (64/90) had intermediate susceptibility to penicillin (MIC values: 0.125 and 0.25 mg/L) and 20% (18/90) were susceptible to penicillin (MIC values: ≤ 0.064 mg/L). All isolates tested susceptible to ceftriaxone, ciprofloxacin and rifampicin.