MRSA - disease prevalence report 2022

MRSA 2022

The number of persons who had methicillin-resistant Staphylococcus aureus (MRSA) detected for the first time in 2022 increased considerably compared with the number observed in the two preceding years. In 2022, a total of 2,996 cases were recorded, compared with 2,714 in 2021, 2,883 in 2020, 3,657 in 2019 cases and 3,669 in 2018, Figure 1. This increase was expected as the lower numbers recorded in the two preceding years were associated with the COVID-19 restrictions, which were lifted in 2022.

Epidemiological classification

Based on presumed mode of infection, MRSA is divided into the following categories: acquired abroad, hospital-acquired, community-acquired and livestock-associated MRSA. In Denmark, livestock MRSA is nearly always caused by the CC398 MRSA type, which is closely associated with live pigs.

Community-acquired MRSA is further divided according to whether the person has had contact to hospitals or the nursing sector (nursing homes, etc.) within the past six months, and whether the person has come into contact (exposure) with a known MRSA-positive person.

Table 1 shows the distribution of notified MRSA cases by presumed mode of transmission.

The majority of the MRSA cases were acquired in Denmark (2,573), whereas infection abroad was stated in 423 cases (14%). During the COVID-19 epidemic in 2020-21, this share was lower; but prior to COVID-19, the share fell in the 15-20% range. The number of hospital-acquired MRSA cases recorded was only 55 (54 in 2021 and 70 in 2020) and thus continues to comprise only a limited share of the total number of cases (1.8%). Community-acquired MRSA cases with no contact to hospitals or to the nursing sector comprised 1,430 cases in 2022 (48%). In 653 of these cases (46%), there was known exposure to a person with MRSA; in the overwhelming majority of cases, a member of the household (99%). The number of livestock MRSA CC398 cases was 828, which is the lowest number recorded since 2013 (N = 643), comprising 28% of the total number of MRSA cases.

Infections

In 1,514 cases (51%), sampling was performed due to clinical infection. This is in line with the number recorded in the period before COVID-19 (1,599 in 2019, 1,478 in 2018 and 1,471 in 2017). In 50 cases, MRSA was isolated from blood, corresponding to 1.9% of all S. aureus bacteraemia cases, which is in line with recent years. Among the hospital-acquired cases, 30 patients were diagnosed with infection (55%), whereas 20 healthcare staff (71%) had MRSA infection detected. The number of infections among the imported cases increased from 151 in 2021 to 279 in 2022.

This is in line with the level recorded in 2015 (N = 273), but lower than in 2016-2019, Figure 2. The number of community-acquired infections with no healthcare contact was 765. This is the highest number recorded following two years with considerably fewer cases, owing to the COVID-19 restrictions. In 99 cases of community-acquired infection, there was known exposure to MRSA, Table 1.

The number of community-acquired infections with reported contact to a hospital or to the nursing sector within the previous six months was 184 in 2022 compared with 181 in 2021, 159 in 2020 and 174 in 2019, Figure 2.

Typing

MRSA of the CC398 type was detected using specific PCR analysis, which also showed if the strain was of the livestock MRSA type (n = 828) or the human variant (n = 25). Isolates with a characteristic livestock MRSA CC398 profile were typically not spa typed, whereas all other isolates were typed.

The remaining 2,143 isolates represented 357 spa types from 24 different clonal complexes (CC groups). The ten most frequently observed spa types comprised 28% of the isolates. Among these, the five most frequently observed types were t304/CC6 (N=229), t127/CC1 (N=168), t223/CC22 (N=122), t002/CC5 (N=121) and t008/CC8 (N=110).

Outbreaks

Statens Serum Institut offers whole-genome sequencing of all outbreak isolates, i.e. characterisation of the isolates beyond spa-type determination. If an outbreak was caused by a clone within a commonly occurring spa type, whole-genome sequencing may be an important means for identifying and limiting the outbreak. Thereby, the exact extent of the outbreak may be determined more precisely. Via the notification forms, collaboration with the local MRSA units and typing of the submitted isolates, a total of 38 outbreaks were identified at hospitals, nursing homes and other institutions.

These outbreaks comprised a total of 143 MRSA cases, including 70 with infection and 73 detected by screening and infection tracing. Most of the outbreaks counted 1-5 patients. Among the 38 outbreaks, six occurred in neonatal departments. Five outbreaks started in previous years, and more patients were then detected in the course of 2022. The largest number of cases (n = 24) was recorded for an outbreak of spa type t127/CC1, comprising several hospitals in the Greater Copenhagen Area. Additionally, 16 outbreaks occurred at nursing homes or were related to home care nursing (a total of 44 patients) and seven outbreaks occurred at other non-neonatal hospital departments (17 patients).

Livestock MRSA CC398

The number of livestock MRSA CC398 cases (N = 828) was the lowest recorded since 2013 when 643 cases were registered. A total of 230 (28%) patients had a clinical infection at the time of their diagnosis, compared with 271 (28%) in 2021, Table 1.

A total of 84% of the cases were found in persons with direct contact with pigs or in household members to these persons. A total of 131 (16%) persons had no known contact to animals. Among these, 92 had a clinical infection. Contact to livestock, particularly pigs, is the primary source of infection with livestock MRSA in humans. The share of infected persons with no known contact with livestock is in line with the number recorded in recent years and therefore does not indicate any substantial new route of infection for livestock MRSA for humans in Denmark. In 2022, a total of seven cases of bacteraemia with livestock-MRSA CC398 were observed. Three patients died in the 30 days following their sampling date.

MRSA may also be detected in other household animals than pigs, including horses and cattle, in particular, but also in sheep and goats. The MRSA prevalence in farms of these types is much lower than in pig farms. Furthermore, hedgehogs are a natural reservoir for the mecC variant of MRSA. Detection of MRSA in humans with contact to other animals than pigs was limited in 2022 and comprised 10 patients with contact to cattle, four with previous contact to mink, three with contact to horses and only three mecC MRSA patients with reported contact to hedgehogs.

Imported MRSA cases

The number of imported cases was 423, which is higher than the number of imported cases observed in the two preceding years (254 in 2021 and 351 in 2020). This number corresponds to 14% of the total number of cases. Findings of MRSA in asylum seekers has been stated separately since 2015 as they frequently arrive from areas with a high MRSA incidence. Year 2022 recorded a total of 48 new MRSA cases among asylum seekers and people who were family reunified, which is a considerably lower number than in 2016 (417), 2017 (119) and also lower than the number recorded in 2018 (44), 2019 (28), 2020 (24) and 2021 (17).

Handling of MRSA in primary healthcare

Patients with known MRSA colonisation/carrier state have the same rights to work-up and treatment as all other patients and may be seen and treated at any time within the opening hours of the clinic.

General infectious hygiene guidelines are followed during interviews, work-up and treatment. Read more in Guideline on MRSA Prevention and the included infectious hygiene appendices, one of which specifically addresses clinics, including dental clinics.

Work-up and treatment of MRSA

MRSA carrier state is treatable. Read about treatment of MRSA carrier state.

Treatment of an MRSA infection is always preceded by a test for antimicrobial susceptibility to ensure that the patient receives relevant antimicrobial treatment. Read about treatment of MRSA infections.

Swabbing for MRSA is conducted in patients with symptomatic infection that may have been caused by staphylococci and who have been in a risk situation within the past six months. Read more about MRSA risk situations.

MRSA is transmitted by direct and indirect contact. Read more about how to prevent the infection from spreading.

Various information materials are available for patients who have had MRSA detected

Information for persons who have had MRSA detected

Guide for parents to children aged 0-2 years of age who have had MRSA detected.

Information for patients about treatment of MRSA is available in various languages, including Lithuanian, Polish, Romanian and Ukrainian, at the MRSA site of the Danish Health Authority.

Livestock MRSA

MRSA CC398 is a special type of MRSA found in animals that may be transmitted to humans. In Denmark, MRSA CC398 is mainly found in pigs. Read about livestock MRSA.

Information about livestock MRSA

The information about livestock MRSA is available in several languages

MRSA is described in the SSI Disease Encyclopaedia and, in more detail, in this section on antimicrobial resistance.

This report is also described in EPI-NEWS no. 34/2023.