To Örebro University

Invasive meningococcal disease (IMD) is notifiable in Sweden. The reporting system comprises of mandatory notification of cases and mandatory laboratory notification of samples to the Public Health Agency of Sweden, Stockholm. All samples are sent to the National Reference Laboratory for Pathogenic Neisseria, Örebro for further typing and surveillance.

In 2016, 62 cases of IMD (incidence 0.6/100 000 population) were reported in Sweden. Among the patients 58 % were females and 42 % males, aged from 1 month to95 years with mean age of 42 years. The incidence was highest, as in previous years, in the age group 15-19 years (2.1/100 000 population) followed by elderly ≥80 years (1.8/100 000 population) and infants ≤1 year (1.7/100 000 population). The case fatality rate increased in 2016 to 12.9 % compared with 7.5 % in 2015, eight people died from the disease (MenW, n=3; MenY, n=2; MenB, n=2 and MenC n=1). None of the IMD cases in 2016 had any epidemiological linkage.

All 62 cases of IMD were laboratory confirmed: 54 were culture-confirmed, three PCR-confirmed and in five cases further typing data are missing because no samples were sent to the National Reference Laboratory for Pathogenic Neisseria. The serogroup distribution was MenW (n=18, 31.5 %), MenY (n=18, 31.5 %), MenB (n=10, 17.5 %), MenC (n=10, 17.5 %) and one non-groupable isolate. The W:P1.5,2:F1-1:ST11 (cc11) (n=15) were predominant among the culture-confirmed meningococci during 2016 followed by Y:P1.5-2,10-1:F4-1:ST23 (cc23) (n=7) och Y:P1.5-1,2-2:F5-8:ST23 (cc23) (n=6). Antibiotic susceptibility testing was performed with Gradient test (Etest, BioMerieux). Decreased susceptibility to penicillin was seen in 30 % of the isolates (MIC >0,064 mg/L) of which one was resistant (MIC=0.5 mg/L). One of the isolates with decreased susceptibility to penicillin was also resistant to ciprofloxacin (MIC=0.125 mg/L). All other isolates were susceptible to cefotaxime, chloramphenicol, ciprofloxacin, rifampicin and meropenem. No β-lactamase producing isolates has so far been found in Sweden.

To conclude, the incidence of IMD continues to be relatively low in Sweden, however, a shift in the serogroup distribution of N. meningitidisin Sweden is ongoing; the previously dominating disease-causing MenB and MenC have been replaced, first by MenY which emerged in 2009 and since 2015 also by MenW. MenW has gone from only causing invasive disease in a few, 0-6 cases per year from 1990 onwards, to now being the dominating serogroup together with MenY in Sweden 2016.