Methicillin-resistant Staphylococcus aureus epidemic restricted to one health district in Finland: a population-based descriptive study in Pirkanmaa, Finland, years 2001-2011

Community methicillin-resistant Staphylococcus aureus outbreaks in areas of low prevalence

BACKGROUND

Community-acquired (CA), community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) infection presents a significant public health challenge, even where MRSA rates are historically lower. Despite successes in reducing hospital-onset MRSA, CO-MRSA rates are increasing globally, with a need to understand this trend, and the potential risk factors for re-emergence.

OBJECTIVES

This review aims to explore the characteristics of outbreaks of community-acquired community-onset methicillin-resistant Staphylococcus aureus in low-prevalence areas, to understand the factors involved in its rise, and to translate this knowledge into public health policy and further research needs.

SOURCES

PubMed, EMBASE, and Google Scholar were searched using combinations of the terms 'transmission', 'acquisition', 'community-acquired', 'MRSA', 'CA-MRSA', 'low prevalence', 'genomic', 'outbreak', 'colonisation', and 'carriage'. Wherever evidence was limited, additional articles were sought specifically, via PubMed searches. Papers where materials were not available in English were excluded.

CONTENT

Challenges in defining low-prevalence areas and the significance of exposure to various risk factors for community acquisition, such as healthcare settings, travel, livestock, and environmental factors, are discussed. The importance of genomic surveillance in identifying outbreak strains and understanding the transmission dynamics is highlighted, along with the need for robust public health policies and control measures.

IMPLICATIONS

The findings emphasise the complexity of CO-MRSA transmission and the necessity of a multifaceted approach in low-prevalence areas. This includes integrated and systematic surveillance of hospital-onset-, CO-, and livestock-associated MRSA, as has been effective in some Northern European countries. The evolution of CO-MRSA underscores the need for global collaboration, routine genomic surveillance, and comprehensive antimicrobial stewardship to mitigate the rise of CO-MRSA and address the broader challenge of antimicrobial resistance. These efforts are crucial for maintaining low MRSA prevalence and managing the increasing burden of CO-MRSA in both low and higher prevalence regions.

Increasing Incidences and Clonal Diversity of Methicillin-Resistant Staphylococcus aureus in the Nordic Countries - Results From the Nordic MRSA Surveillance

Methicillin-resistant Staphylococcus aureus (MRSA) is notifiable in Denmark, Finland, Iceland, Norway and Sweden. The prevalence of MRSA in this region has been low for many years, but all five countries experience increasing numbers of new cases. The aim of the study was to describe the molecular epidemiology in the Nordic countries 2009-2016. Numbers of new cases of MRSA from 1997 to 2016 were compared, and a database containing information on spa-type and place of residence or acquisition, for all new MRSA isolates from 2009 to 2016 was established. A website was developed to visualize the geographic distribution of the spa-types. The incidence of new MRSA cases increased in all Nordic countries with Denmark having 61.8 new cases per 100,000 inhabitants in 2016 as the highest. The number of new cases 2009 to 2016 was 60,984. spa-typing revealed a high genetic diversity, with a total of 2,344 different spa-types identified. The majority of these spa-types (N = 2,017) were found in 1-10 cases. The most common spa-types t127/CC1, t223/CC22, and t304/CC6:8 increased significantly in all Nordic countries during the study period, except for Iceland, while spa-type t002/CC5 decreased in the same four countries. The trends of other common spa-types were different in each of the Nordic countries. The Nordic countries were shown to share similar trends but also to have country-specific characteristics in their MRSA populations. A continued increasing numbers of MRSA will challenge the surveillance economically. A more selected molecular surveillance will probably have to be employed in the future.

Spa type distribution in MRSA and MSSA bacteremias and association of spa clonal complexes with the clinical characteristics of bacteremia

The genetic distribution of invasive methicillin-susceptible (MSSA) and resistant S. aureus (MRSA) strains has to be addressed in order to target infection control strategies. A large MRSA epidemic caused by a certain MRSA strain (spa type 067) broke out in 2001 in our health district. We wanted to investigate the current spa type distribution in MRSA and MSSA bacteremias and assess the potential association of spa clonal complexes (spaCC) with the clinical characteristics of S. aureus bacteremia. One hundred nine invasive MRSA isolates and 353 invasive MSSA isolates were spa typed and grouped into clonal complexes (spaCC). Spa type distribution was compared to that of colonizing MRSA strains. Spa type and spaCC data linked to clinical information on the course of bacteremic cases was used to search for differences in virulence between strains. Spa type distribution in MRSA is less heterogenic than in MSSA. t067 dominates both in MRSA colonisations and in invasive findings. Among MSSA, no such dominating strains were found. Of spaCCs, mortality was the highest in spaCC 067 (25.6%). SpaCC 008 was more often associated with endocarditis than other CCs (22.7 vs 5.8%, p = 0.013), spaCC 2133 with skin infections (68.4 vs 36.4%, p = 0.007), and spaCC 012 with foreign body infections (25.0 vs 9.3%, p = 0.029) than other clonal complexes. A single successful strain can explain the major proportion of MRSA among S. aureus bacteremias. Certain spaCCs showed association with certain clinical characteristics. These findings suggest that S. aureus strains differ in their virulence and invasiveness.

Trends in incidence and resistance patterns of Staphylococcus aureus bacteremia. Infect Dis (Lond) 2017;50:52-58. [PMID: 29161942 DOI: 10.1080/23744235.2017.1405276]

BACKGROUND

Staphylococcus aureus bacteremia (SAB) causes a significant burden on the population. Several infection control measures have been implemented in Pirkanmaa county to combat a local epidemic with methicillin-resistant Staphylococcus aureus (MRSA). We aimed to study the epidemiology of SAB and antibiotic resistance of S. aureus and the possible influence of improved infection control.

METHODS

Register data from 2005 to 2015 were retrospectively analysed to study the antimicrobial susceptibility, the incidence and mortality in SAB in a population-based setting.

RESULTS

The incidence of SAB increased during the study period from 21.6 to 35.8/100,000 population. The number of both health care-associated (HA) and community-associated (CA) cases has increased. The incidence of MSSA bacteremia increased from 19.9 to 35.2/100,000 population in Pirkanmaa in parallel to other parts of Finland. The incidence of MRSA bacteremia was 10-fold (4.5/100,000 population) higher in 2011 than in other parts of the country, but sank to the national level (0.59/100,000 population) in 2015. The fatality rate decreased from 22% to 17%. The proportion of penicillin-susceptible Staphylococcus aureus (PSSA) increased from 23.9% in 2008 to 43.1% in 2015.

CONCLUSION

The incidence of both HA and CA SAB has increased since 2005. Conversely, the proportion of MRSA and PRSA bacteremia has decreased. Promotion of infection control measures may have reduced the incidence of MRSA bacteremia but not the overall incidence of SAB. The rising proportion of PSSA enables the use of targeted, narrow spectrum antimicrobials.

Comparison of outcome and clinical characteristics of bacteremia caused by methicillin-resistant, penicillin-resistant and penicillin-susceptible Staphylococcus aureus strains

BACKGROUND

The aim of this study was to assess the association of methicillin resistance and penicillinase production with clinical characteristics and outcome of Staphylococcus aureus bacteremia.

METHODS

For 126 patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, 378 age- and gender-matched controls with methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia were selected. Of controls, 126 had bacteremia caused by penicillin-susceptible strains (PSSA) and 252 by penicillinase-producing strains (PRSA). Underlying diseases, clinical course and mortality were retrospectively assessed.

RESULTS

Patients with MRSA bacteremia were more often smokers than patients with MSSA bacteremia (OR 2.34, 95% CI 1.27-4.32). MRSA bacteremia was more often healthcare-associated (OR 4.23, 95% CI 2.47-7.24), associated with central venous catheters (OR 2.09, 95% CI 1.27-3.47), glucocorticoid therapy (OR 1.82, 95% CI 1.12-2.93) and prior surgery (OR 2.32, 95% CI 1.43-3.76). Patients with MRSA bacteremia received appropriate empiric antibiotic (31%) less often than controls (98%). Mortality within 28 days was higher in MRSA bacteremia (26.8%) than in MSSA bacteremia (15.5%) (OR 2.00, 95% CI 1.20-3.34), PRSA bacteremia (17.0%) (OR 1.79 95% CI 1.04-3.09) or PSSA bacteremia (12.5%) (OR 2.56 95% CI 1.27-5.15). The difference remained after adjusting for underlying diseases and foci. There was no significant difference in clinical course between PRSA and PSSA bacteremias.

CONCLUSIONS

MRSA bacteremia was associated with poorer outcome than either PRSA or PSSA bacteremia. We corroborated several risk factors found in previous studies.

Combined interventions are effective in MRSA control

BACKGROUND

A large healthcare-associated epidemic mainly caused by one methicillin-resistant Staphylococcus aureus (MRSA) strain broke out in Pirkanmaa County, Finland, in 2001. This study describes the impact of infection control and screening practices on the epidemic.

METHODS

The number of hospital-acquired (HA)-MRSA findings obtained from clinical and screening samples during the epidemic was calculated. Strains were typed by pulsed-field electrophoresis (PFGE) or spa typing. Strain type distribution was studied in relation to sample type, year of the epidemic and site of transmission. Several infection control interventions were launched stepwise and screening protocols were expanded.

RESULTS

A total of 4118 cases were identified during 2001-2014, of which 3527 were classified as HA. One strain (spa t067) dominated in the epidemic. HA-MRSA cases decreased constantly from the year 2011. The number of new HA-MRSA cases was 57% less in the year 2014 (n = 171) as compared with the year 2011 (n = 399). The proportion of the epidemic strain declined significantly over the years. Screening samples comprised 71% (2439/3527) and clinical samples 29% (1034/3527) of HA-MRSA findings. The number of HA-MRSA cases found from clinical samples started to decrease when screening was expanded. An increase in hand-rub consumption was associated with a decrease in transmissions in Tampere University Hospital (TAUH).

CONCLUSION

Implementation of universal screening together with several other interventions is effective in containing an MRSA epidemic. The proportion of other than Pirkanmaa epidemic (PE)-MRSA strain findings increased throughout the period, indicating the changing epidemiology of MRSA.

The dynamic changes of dominant clones of Staphylococcus aureus causing bloodstream infections in the European region: results of a second structured survey

Staphylococcus aureus is one of the most important human pathogens and meticillin-resistant S. aureus (MRSA) presents a major cause of healthcare- and community-acquired infections. This study investigated the spatial and temporal changes of S. aureus causing bacteraemia in Europe over a five-year interval and explored the possibility of integrating pathogen-based typing data with epidemiological and clinical information at a European level. Between January 2011 and July 2011, 350 laboratories serving 453 hospitals in 25 countries collected 3,753 isolates (meticillin-sensitive S. aureus (MSSA) and MRSA) from patients with S. aureus bloodstream infections. All isolates were sent to the national staphylococcal reference laboratories and characterised by quality-controlled spa typing. Data were uploaded to an interactive web-based mapping tool. A wide geographical distribution of spa types was found, with some prevalent in all European countries. MSSA was more diverse than MRSA. MRSA differed considerably between countries with major international clones expanding or receding when compared to a 2006 survey. We provide evidence that a network approach of decentralised typing and visualisation of aggregated data using an interactive mapping tool can provide important information on the dynamics of S. aureus populations such as early signalling of emerging strains, cross-border spread and importation by travel.

Nosocomial bloodstream infections in a Finnish tertiary care hospital: a retrospective cohort study of 2175 episodes during the years 1999-2001 and 2005-2010

BACKGROUND

Nosocomial infections are major causes of morbidity in hospitalized patients.

METHODS

Retrospective laboratory-based surveillance during 1999-2001 and 2005-2010 identified 2175 cases of nosocomial bloodstream infections (BSIs) in Tampere University Hospital (TAUH), Finland.

RESULTS

Analysis revealed that 57% of BSIs were caused by a gram-positive organism, 27% by a gram-negative organism, 5% by a fungal organism, and 11% were polymicrobial. The most common cause of nosocomial BSI was coagulase-negative staphylococci (23%). Candida species caused 5% of the infections. The 7-day and 30-day case fatalities were 8% (161/2158) and 15% (313/2175), respectively, and were highest in BSIs caused by Candida albicans (22% and 44%) and Pseudomonas aeruginosa (17% and 25%). The median age of patients was 54 years in 1999-2001, 57 years in 2005-2007, and 60 years in 2008-2010 (p < 0.001). The median time from hospital admission to the onset of BSI was 11 days (quartiles 5-18 days). This period was shortest for Streptococcus agalactiae BSI and longest for Candida non-albicans fungemia (1 vs 19 days). The case fatality rate in nosocomial BSI decreased during the years studied: 7-day and 30-day case fatalities were 9% and 16% during 1999-2001, 8.5% and 16% during 2005-2007, and 5% and 12% during 2008-2010, respectively (p < 0.003 and p = 0.022, respectively).

CONCLUSIONS

Gram-positive infections predominate in nosocomial BSIs. The median age of patients with nosocomial BSI has risen during the study years. The case fatality associated with nosocomial BSI has decreased.