Invasive meningococcal disease (IMD) is a notifiable disease in Australia, with both probable and laboratory-confirmed cases of IMD reportable to the National Notifiable Diseases Surveillance System (NNDSS). In 2021, there were 74 notifications of IMD made, the lowest number recorded since 1991 when records began. Ninety-one percent of notified cases (67/74) were laboratory confirmed, with 69% of laboratory-confirmed cases (46/67) diagnosed by bacterial culture and 31% (21/67) by nucleic acid amplification testing. The serogroup was determined for 63/67 laboratory-confirmed cases (94%): serogroup B (MenB) accounted for 52% of infections (35/67); MenW for 22% (15/67); MenY for 19% (13/67); there were no infections attributed to MenC. Fine typing was available on 37/67 (55%) where the serogroup was determined. The greatest variability was in MenB, with nine different porA types represented. All MenW infections belonged to a single porA type (P1.5,2) with five different MLST sequence types represented: 11, 574, 1287, 12351, 13135; all belonged to clonal complex 11, the hypervirulent strain reported in recent outbreaks in Australia and overseas. All MenY were from the same porA antigen type, P1.5-1,10-1: MLST sequence type 1655; clonal complex 23. Peaks occurred in children less than 5 years, reaching 24% (16/67) of reported cases, and in those aged 15-19 years reaching 16% (11/67) of reported cases. It is notable that 15% (10/67) of notifications were in persons aged 45-64 years, and an equivalent proportion (15%; 10/67) in adults aged 65 years and above. MenB infections predominated in persons aged 15-19 years (100%, 11/11), and comprised 56% (9/16) of infections in children aged less than 5 years. By contrast, Men W infections accounted for half (5/10) of IMD detections in infants less than 1 year, and 30% (3/10) of infections in persons aged 45-65 years. MenY infections predominated in adults aged 65 years and greater, resulting in 70% (7/10) of IMD in this age group. All 46 IMD isolates had antimicrobial susceptibility testing performed. Minimum inhibitory concentration (MIC) values were categorised using Clinical Laboratory Standards Institute (CLSI) interpretative criteria: 13% (6/46) were defined as penicillin resistant (MIC value, ≥ 0.5 mg/L); 59% (27/46) had intermediate susceptibility to penicillin (MIC values, 0.125 and 0.25 mg/L) and 28% (13/46) were susceptible to penicillin. All isolates were susceptible to ceftriaxone and rifampicin. A single MenB IMD isolate from New South Wales exhibited ciprofloxacin resistance (MIC value, 0.125 mg/L).
Keywords: Neisseria meningitidis; antimicrobial resistance; disease surveillance; invasive meningococcal disease.
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