Campylobacteriosis in Finland: Passive Surveillance in 2004-2021 and a Pilot Case-Control Study with Whole-Genome Sequencing in Summer 2022

Campylobacteriosis causes a significant disease burden in humans worldwide and is the most common type of zoonotic gastroenteritis in Finland. To identify infection sources for domestic Campylobacter infections, we analyzed Campylobacter case data from the Finnish Infectious Disease Register (FIDR) in 2004-2021 and outbreak data from the National Food- and Waterborne Outbreak Register (FWO Register) in 2010-2021, and conducted a pilot case-control study (256 cases and 756 controls) with source attribution and patient sample analysis using whole-genome sequencing (WGS) in July-August 2022. In the FIDR, 41% of the cases lacked information on travel history. Based on the case-control study, we estimated that of all cases, 39% were of domestic origin. Using WGS, 22 clusters of two or more cases were observed among 185 domestic cases, none of which were reported to the FWO register. Based on this case-control study and source attribution, poultry is an important source of campylobacteriosis in Finland. More extensive sampling and comparison of patient, food, animal, and environmental isolates is needed to estimate the significance of other sources. In Finland, campylobacteriosis is more often of domestic origin than FIDR notifications indicate. To identify the domestic cases, travel information should be included in the FIDR notification, and to improve outbreak detection, all domestic patient isolates should be sequenced.

Invasive listeriosis in Finland: surveillance and cluster investigations, 2011-2021

Foodborne pathogen Listeria monocytogenes may cause serious, life-threatening disease in susceptible persons. We combined data from Finnish national listeriosis surveillance, patient interview responses, and laboratory data of patient samples and compared them to listeria findings from food and food production plants collected as part of outbreak investigations during 2011-2021. The incidence of invasive listeriosis in Finland (1.3/100000 in 2021) is higher than the EU average (0.5/100000 in 2021), and most cases are observed in the elderly with a predisposing condition. Many cases reported consuming high-risk foods as well as improper food storage. Since ongoing patient interviews and whole genome sequencing were introduced, several listeriosis outbreaks were detected and food sources identified. Recommendations about high-risk foods for listeriosis and proper food storage should be better communicated to susceptible people. In Finland, patient interviews and typing and comparing listeria isolates in foods and patient samples are crucial in solving outbreaks and determining measures to control invasive listeriosis.

Shiga toxin-producing Escherichia coli (STEC) stool multiplex PCR can replace culture for clinical diagnosis and follow-up

Shiga toxin (stx)-producing Escherichia coli (STEC) causes potentially severe gastrointestinal infections. Due to its public health importance, control measures are required, and carriers may need to refrain from work or daycare when the risk of spread to vulnerable people is high. We evaluated the use of direct stool multiplex PCR compared to culture for primary STEC diagnostics and for follow-up in order to update the national guidelines for STEC monitoring. We analyzed primary and follow-up samples of 236 STEC PCR-positive cases at HUSLAB, Helsinki, Finland in 2016-2017, altogether 858 samples. All STEC PCR-positive samples were inoculated on non-selective chromogenic agar plates. Culture positivity was confirmed from culture sweeps by PCR. 211 (89%) of the cases were culture positive in their primary sample. Of all primary and follow-up samples, 499 were PCR positive and of these 450 (90%) were culture positive. PCR-negative follow-up samples were available from 125 cases. Of these, 88 cases were followed for at least three consecutive PCR-negative samples. Two cases (2%) had culture-positive sample(s) after two consecutive PCR-negative samples. The median time for STEC clearance was 22-23 days. The laboratory-developed multiplex PCR test used in this study is a reliable method for STEC diagnostics and follow-up in a clinical laboratory. When non-selective methodology is used, the majority of PCR-positive samples (90%) are also culture positive. Furthermore, only two cases (2%) in our material had two consecutive PCR-negative samples followed by positive samples. Consequently, to demonstrate the clearance from STEC infection, we consider two PCR-negative follow-up samples sufficient. The Finnish national guidelines for STEC monitoring have been updated accordingly.

Epidemiological and microbiological investigation of a large increase in vibriosis, northern Europe, 2018

BackgroundVibriosis cases in Northern European countries and countries bordering the Baltic Sea increased during heatwaves in 2014 and 2018.AimWe describe the epidemiology of vibriosis and the genetic diversity of Vibrio spp. isolates from Norway, Sweden, Denmark, Finland, Poland and Estonia in 2018, a year with an exceptionally warm summer.MethodsIn a retrospective study, we analysed demographics, geographical distribution, seasonality, causative species and severity of non-travel-related vibriosis cases in 2018. Data sources included surveillance systems, national laboratory notification databases and/or nationwide surveys to public health microbiology laboratories. Moreover, we performed whole genome sequencing and multilocus sequence typing of available isolates from 2014 to 2018 to map their genetic diversity.ResultsIn 2018, we identified 445 non-travel-related vibriosis cases in the study countries, considerably more than the median of 126 cases between 2014 and 2017 (range: 87-272). The main reported mode of transmission was exposure to seawater. We observed a species-specific geographical disparity of vibriosis cases across the Nordic-Baltic region. Severe vibriosis was associated with infections caused by Vibrio vulnificus (adjOR: 17.2; 95% CI: 3.3-90.5) or Vibrio parahaemolyticus (adjOR: 2.1; 95% CI: 1.0-4.5), age ≥ 65 years (65-79 years: adjOR: 3.9; 95% CI: 1.7-8.7; ≥ 80 years: adjOR: 15.5; 95% CI: 4.4-54.3) or acquiring infections during summer (adjOR: 5.1; 95% CI: 2.4-10.9). Although phylogenetic analysis revealed diversity between Vibrio spp. isolates, two V. vulnificus clusters were identified.ConclusionShared sentinel surveillance for vibriosis during summer may be valuable to monitor this emerging public health issue.

Shopping Detail Information and Home Freezer Sampling Confirmed the Role of Commercial, Modified-Atmosphere Packaged Meatballs as a Vehicle for Listeriosis in Finland

In November 2016, an elderly patient was diagnosed with Listeria monocytogenes bacteremia in Finland. Grocery store loyalty card records and microbiological investigation of foods found in the home fridge and freezer of the patient revealed commercial, modified-atmosphere packaged meatballs as the source of the infection. Investigation of the meatball production plant revealed that the floor drain samples were contaminated with the same L. monocytogenes strain as those isolated from the patient and meatballs. Ready-to-eat meatballs were likely contaminated after heat treatment from the production environment before packaging. Long-term cold storage, modified-atmosphere conditions, and the absence of competing bacteria presumably enhanced the growth of L. monocytogenes. We recommend that collection of shopping details and home fridge and freezer sampling should be part of surveillance of all cases of L. monocytogenes infections to complement information obtained from in-depth interviews.

Outbreak of multiple strains of non-O157 Shiga toxin-producing and enteropathogenic Escherichia coli associated with rocket salad, Finland, autumn 2016

In August 2016, an outbreak of Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) with 237 cases occurred in the Helsinki metropolitan area, Finland. Gastroenteritis cases were reported at 11 events served by one catering company. Microbiological and epidemiological investigations suggested rocket salad as the cause of the outbreak.

STEC ONT

H11 and EPEC O111:H8 strains isolated from food samples containing rocket were identical to the patient isolates. In this outbreak, the reported symptoms were milder than considered before for STEC infection, and the guidelines for STEC control measures need to be updated based on the severity of the illness. Based on our experience in this outbreak, national surveillance criteria for STEC have been updated to meet the practice in reporting laboratories covering both PCR-positive and culture-confirmed findings. We suggest that EPEC could be added to the national surveillance since diagnostics for EPEC are routinely done in clinical laboratories.

Heat Wave-Associated Vibriosis, Sweden and Finland, 2014

During summer 2014, a total of 89 Vibrio infections were reported in Sweden and Finland, substantially more yearly infections than previously have been reported in northern Europe. Infections were spread across most coastal counties of Sweden and Finland, but unusually, numerous infections were reported in subarctic regions; cases were reported as far north as 65°N, ≈100 miles (160 km) from the Arctic Circle. Most infections were caused by non-O1/O139 V. cholerae (70 cases, corresponding to 77% of the total, all strains were negative for the cholera toxin gene). An extreme heat wave in northern Scandinavia during summer 2014 led to unprecedented high sea surface temperatures, which appear to have been responsible for the emergence of Vibrio bacteria at these latitudes. The emergence of vibriosis in high-latitude regions requires improved diagnostic detection and clinical awareness of these emerging pathogens.

Destination specific risks of acquisition of notifiable food- and waterborne infections or sexually transmitted infections among Finnish international travellers, 1995-2015

BACKGROUND

Overnight international travels made by Finns more than doubled during 1995-2015. To estimate risks and observe trends of travel-related notifiable sexually transmitted and food- and water-borne infections (STIs and FWIs) among travellers, we analysed national reports of gonorrhoea, syphilis, hepatitis A, shigellosis, campylobacteriosis and salmonellosis cases and related them to travel statistics.

METHOD

Cases notified as travel-related to the Finnish infectious diseases register were used as numerators and overnight stays of Statistics Finland surveys as denominator. We calculated overall risks (per 100,000 travellers) and assessed trends (using regression model) in various geographic regions.

RESULTS

Of all travel-related cases during 1995-2015, 2304 were STIs and 70,929 FWIs. During 2012-2015, Asia-Oceania showed highest risk estimates for gonorrhoea (11.0; 95%CI, 9.5-13), syphilis (1.4; 0.93-2.1), salmonellosis (157; 151-164), and campylobacteriosis (135; 129-141), and Africa for hepatitis A (4.5; 2.5-7.9), and shigellosis (35; 28-43). When evaluating at country level, the highest risks of infections was found in Thailand, except for hepatitis A ranking Hungary the first. During 2000-2011, significantly decreasing trends occurred for most FWIs particularly in the European regions and for STIs in Russia-Baltics.

CONCLUSIONS

Our findings can be used in targeting pre-travel advice, which should also cover those visiting Thailand or European hepatitis A risk areas.

Severe Outbreak of Sorbitol-Fermenting Escherichia coli O157 via Unpasteurized Milk and Farm Visits, Finland 2012

Shiga toxin-producing, sorbitol-fermenting Escherichia coli O157 (SF O157) has emerged as a cause of severe human illness. Despite frequent human findings, its transmission routes and reservoirs remain largely unknown. Foodborne transmission and reservoir in cattle have been suspected, but with limited supporting evidence. This study describes the outbreak of SF O157 that occurred in Finland in 2012. The outbreak originated from a recreational farm selling unpasteurized milk, as revealed by epidemiologic and microbiological investigations, and involved six hospitalized children and two asymptomatic adults with culture-confirmed infection. An identical strain of SF O157 was isolated from patients, cattle and the farm environment, and epidemiologic analysis suggested unpasteurized milk as the vehicle of transmission. This study reports the first milkborne outbreak of SF O157, provides supporting evidence of cattle as a reservoir and highlights the health risks related to the consumption of unpasteurized milk.

Heat Wave-Associated Vibriosis, Sweden and Finland, 2014

During summer 2014, a total of 89 Vibrio infections were reported in Sweden and Finland, substantially more yearly infections than previously have been reported in northern Europe. Infections were spread across most coastal counties of Sweden and Finland, but unusually, numerous infections were reported in subarctic regions; cases were reported as far north as 65°N, ≈100 miles (160 km) from the Arctic Circle. Most infections were caused by non-O1/O139 V. cholerae (70 cases, corresponding to 77% of the total, all strains were negative for the cholera toxin gene). An extreme heat wave in northern Scandinavia during summer 2014 led to unprecedented high sea surface temperatures, which appear to have been responsible for the emergence of Vibrio bacteria at these latitudes. The emergence of vibriosis in high-latitude regions requires improved diagnostic detection and clinical awareness of these emerging pathogens.

Outbreak of Yersinia pseudotuberculosis O:1 infection associated with raw milk consumption, Finland, spring 2014

In March 2014, a Yersinia pseudotuberculosis (YP) outbreak was detected by a municipal authority in southern Finland. We conducted epidemiological, microbiological and traceback investigations to identify the source. We defined a case as a person with YP infection notified to the National Infectious Disease Registry between February and April 2014, or their household member, with abdominal pain and fever≥38 °C or erythema nodosum. Healthy household members were used as household-matched controls. We identified 43 cases and 50 controls. The illness was strongly associated with the consumption of raw milk from a single producer. The odds ratio of illness increased with the amount of raw milk consumed. Also previously healthy adults became infected by consuming raw milk. Identical YP strains were identified from cases' stool samples, raw milk sampled from a case's refrigerator and from the milk filter at the producer's farm. The producer fulfilled the legal requirements for raw milk production and voluntarily recalled the raw milk and stopped its production. We advised consumers to heat the raw milk to 72 °C for 15 s. Current legislation for raw milk producers should be reviewed and public awareness of health risks linked to raw milk consumption should be increased.

Multinational outbreak of Salmonella Enteritidis infection during an international youth ice hockey competition in Riga, Latvia, preliminary report, March and April 2015

A multinational outbreak of salmonellosis linked to the Riga Cup 2015 junior ice-hockey competition was detected by the Finnish health authorities in mid-April and immediately notified at the European Union level. This prompted an international outbreak investigation supported by the European Centre for Disease Prevention and Control. As of 8 May 2015, seven countries have reported 214 confirmed and suspected cases, among which 122 from Finland. The search for the source of the outbreak is ongoing.

Occurrence and characterization of methicillin-resistant staphylococci from bovine mastitis milk samples in Finland

Background

Methicillin-resistant staphylococci (MRS) are increasingly being isolated in bovine mastitis. The aim of our study was to evaluate the occurrence of MRS in Finnish mastitis milk samples and characterize the MRS isolates using molecular methods.

Results

Methicillin-resistant S. aureus (MRSA) was a rare finding in bovine mastitis in Finland. Only two out of 135 (1.5%) S. aureus isolates were positive for mec genes. One of these carried mecA and was of spa type t172, SCCmec type IV and ST375, and the other harboured mecC, being spa type t3256, and ST130. MRSA ST375 is common among human MRSA isolates in Finland, but this is the first report in the country of bovine mecC MRSA. In coagulase-negative staphylococci (CoNS) originating from bovine mastitis, methicillin resistance was more common. In the two CoNS collections studied, 5.2% (17/324) and 1.8% (2/110) of the isolates were mecA positive. Eighteen of these were methicillin-resistant S. epidermidis (MRSE), which were divided into 6 separate PFGE clusters. One pulsotype was detected in different parts of the country, indicating clonal spread. Most MRSE (13/18) were of SCCmec type IV, one was of type V and four were non-typeable. Comparison with a human staphylococcal database indicated that bovine MRSE strains were not closely related to human MRSE isolates.

Conclusions

The occurrence of MRS, especially MRSA, in bovine mastitis in Finland was low. Most methicillin-resistant bovine CoNS are MRSE, and we found evidence of a bovine MRSE strain that may spread clonally. This is the first report of a Finnish bovine isolate of MRSA_mecC ST130. The study provides a baseline for further MRS monitoring.

Adapting spa typing for national laboratory-based surveillance of methicillin-resistant Staphylococcus aureus

Laboratory-based surveillance of methicillin-resistant Staphylococcus aureus (MRSA) monitors the baseline occurrence of different genotypes and identifies strains and transmission chains responsible for outbreaks. The consequences of substituting pulsed-field gel electrophoresis (PFGE) with spa typing as a first-line typing method were analyzed by typing 589 strains isolated between 1997 and 2006, with a focus on both short- and long-term correspondence between the PFGE and spa typing results. The study, covering these ten years, included all Finnish MRSA blood isolates and representatives of the two most prevalent MRSA strains (PFGE types FIN-4 and FIN-16) in Finland. In addition, all sporadic isolates from 2006 were included. spa typing was more expensive but approximately four times faster to perform than PFGE. Nearly 90% of FIN-4 and FIN-16 isolates showed consistent spa types, t172 and t067, respectively. spa typing predicted the PFGE result of the blood isolates by a Wallace coefficient of 0.9009, recognized internationally successful strains (t041, t067) to be common also in Finland, and identified a separate cluster of isolates, also related in time and place among the FIN-4 strains. Additional typing by another method was needed to provide adequate discrimination or to characterize isolates with a newly recognized spa type in Finland.

Human cases of methicillin-resistant Staphylococcus aureus CC398, Finland

Nationwide surveillance identified 10 human isolates of methicillin-resistant Staphylococcus aureus clonal complex (CC) 398. Further typing in comparison with animal isolates identified 4 clusters: 1 related to a horse epidemic and 3 to persons who had no direct contact with animals or each other. These findings may indicate unrecognized community transmission.

Molecular characterization of methicillin-resistant Staphylococcus epidermidis strains from bacteraemic patients

In order to study the clonality of clinical methicillin-resistant Staphylococcus epidermidis (MRSE) strains and their staphylococcal cassette chromosome mec (SCCmec) elements, 60 isolates of MRSE from bacteraemic patients in three units of the Helsinki University Hospital, Finland were selected, covering the periods 1990-1993 and 1997-1998. The MRSE strains were analysed by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing and SCCmec typing. Eleven PFGE types (FIN-SE-1-11) with sequence type ST2 (clonal complex 2; CC2) were identified. The previously established methicillin-resistant Staphylococcus aureus SCCmec criteria were applied to name the MRSE SCCmec complexes, and it was found that 7% of the isolates carried SCCmec type IA (ccrA1, class B), whereas the majority (93%) yielded six non-typeable SCCmec PCR patterns (P1-P6). Within each SCCmec PCR pattern, two ccr recombinase genes (ccrA2 and ccrA3) and two mec gene complexes (class A and class B) were detected. In addition, the ccrC gene was associated with three of the six patterns. In conclusion, the MRSE strains were genetically related to each other (ST2) but their SCCmec complexes were unique combinations of elements previously recognized among SCCmec types III and IV.

Nationwide trends in molecular epidemiology of methicillin-resistant Staphylococcus aureus, Finland, 1997-2004

Background

In Finland, the annual number of MRSA notifications to the National Infectious Disease Register (NIDR) has constantly increased since 1995, and molecular typing has revealed numerous outbreak isolates of MRSA. We analyzed the data on MRSA notifications of the NIDR, and MRSA isolates were identified mainly by pulsed-field gel electrophoresis (PFGE) at the National Reference Laboratory (NRL) in Finland during 1997–2004. One isolate representative of each major PFGE type was further characterized by multilocus sequence (MLST)-, staphylococcal cassette chromosome mec (SCCmec)-, and Panton-Valentine leukocidin (PVL)-typing.

Results

The annual number of MRSA notifications to the NIDR rose over ten-fold, from 120 in 1997 to 1458 in 2004, and the proportion of MRSA among S. aureus blood isolates tripled, from <1% during 1997–2003 to 2.8% in 2004. During the same period of time, 253 different strains among 4091 MRSA isolates were identified by PFGE: 215 were sporadic and 38 outbreak/epidemic strains, including 24 new strains. Two epidemic strains resembling internationally recognized MRSA clones accounted for most of the increase: FIN-16 (ST125:IA) from <1% in 1997 to 25% in 2004, and FIN-21 (ST228:I) from 6% in 2002 to 28% in 2004. Half of the ten most common strains carried SCCmec IV or V.

Conclusion

The predominant MRSA strains seem to change over time, which encourages us to continue implementing active control measures with each new MRSA case.

Panton-Valentine leukocidin genes and staphylococcal chromosomal cassette mec types amongst Finnish community-acquired methicillin-resistant Staphylococcus aureus strains, 1997–1999

Methicillin-resistant Staphylococcus aureus (MRSA) strains from Finland covering years 1997-1999 were studied for the presence of Panton-Valentine leukocidin (PVL) gene loci, and the clinically well-defined community-acquired MRSA (CA-MRSA) strains (n = 108) also for staphylococcal chromosomal cassette mec (SCCmec) and multilocus sequence types (MLST). Only a minority (12%) of the CA-MRSA strains contained the PVL gene loci and possessed genotypes formerly described as typical to CA-MRSA strains. The majority of these strains were heterogenous by MLST and pulsed-field gel electrophoresis (PFGE) analysis but, however, harboured the SCCmec cassette type IV. In conclusion, it seems doubtful to consider only molecular characteristics such as the presence of PVL genes as definite markers for CA-MRSA strains.

Evaluation of molecular typing methods in characterizing a European collection of epidemic methicillin-resistant Staphylococcus aureus strains: the HARMONY collection

We analyzed a representative sample of methicillin-resistant Staphylococcus aureus (MRSA) from 11 European countries (referred to as the HARMONY collection) using three molecular typing methods used within the HARMONY group to examine their usefulness for large, multicenter MRSA surveillance networks that use these different laboratory methodologies. MRSA isolates were collected based on their prevalence in each center and their genetic diversity, assessed by pulsed-field gel electrophoresis (PFGE). PFGE groupings (< or = 3 bands difference between patterns) were compared to those made by sequencing of the variable repeats in the protein A gene spa and clonal designations based on multilocus sequence typing (MLST), combined with PCR analysis of the staphylococcal chromosome cassette containing the mec genes involved in methicillin resistance (SCCmec). A high level of discrimination was achieved using each of the three methodologies, with discriminatory indices between 89.5% and 91.9% with overlapping 95% confidence intervals. There was also a high level of concordance of groupings made using each method. MLST/SCCmec typing distinguished 10 groups containing at least two isolates, and these correspond to the majority of nosocomial MRSA clones described in the literature. PFGE and spa typing resolved 34 and 31 subtypes, respectively, within these 10 MRSA clones, with each subtype differing only slightly from the most common pattern using each method. The HARMONY group has found that the methods used in this study differ in their availability and affordability to European centers involved in MRSA surveillance. Here, we demonstrate that the integration of such technologies is achievable, although common protocols (such as we have developed for PFGE) may also be important, as is the use of centralized Internet sites to facilitate data analysis. PFGE and spa-typing data from analysis of MRSA isolates from the many centers that have access to the relevant equipment can be compared to reference patterns/sequences, and clonal designations can be made. In the majority of cases, these will correspond to those made by the (more expensive) method of choice-MLST/SCCmec typing-and these alternative methods can therefore be used as frontline typing systems for multicenter surveillance of MRSA.

Bacterial genotype affects the manifestation and persistence of bovine Staphylococcus aureus intramammary infection

Two-hundred seventeen Staphylococcus aureus isolates from 116 dairy cows with intramammary infections were analyzed by pulsed-field gel electrophoresis to study the association between symptom severity, persistence of infection, and bacterial genotype. Among five main genotypes infecting 90% of the cows, one was associated with severe clinical symptoms but reduced persistence.

Comparison of genotypes of methicillin-resistant and methicillin-sensitive Staphylococcus aureus in Finland

The frequency of horizontal transfer of the staphylococcal cassette chromosome mec to methicillin-susceptible Staphylococcus aureus is unknown. In order to gain more information regarding this frequency in Finland, the genotypes of 299 clinical methicillin-sensitive Staphylococcus aureus isolates were compared to representatives of 24 epidemic methicillin-resistant Staphylococcus aureus genotypes. Sixty-eight percent of the methicillin-sensitive isolates had a genotype similar to eight of the epidemic methicillin-resistant strains. The remaining isolates (32%) showed 22 different genotypes. The results indicate that, in Finland, several methicillin-sensitive Staphylococcus aureus genotypes may have acquired the staphylococcal cassette chromosome mec.

Clustering of Serratia marcescens infections in a neonatal intensive care unit

OBJECTIVES

To study clusters of infections caused by Serratia marcescens in a neonatal intensive care unit (NICU) and to determine risk factors for S. marcescens infection or colonization.

DESIGN

Genotyping of S. marcescens isolates was performed by pulsed-field gel electrophoresis (PFGE). A retrospective case-control study was conducted.

SETTING

A tertiary-care pediatric hospital with a 16-bed NICU.

PATIENTS

All neonates with at least one culture positive for S. marcescens in the NICU during December 1999 to July 2002. Case-patients (n = 11) treated in the NICU during December 1999 to February 2000 were included in the case-control study. Neonates treated in the NICU for at least 72 hours during the same period with cultures negative for S. marcescens were used as control-patients (n = 27).

RESULTS

S. marcescens was cultured from 19 neonates; 9 were infected and 10 were colonized. PFGE analysis identified three epidemic strains; each cluster consisted of identical isolates, except one isolate in the first cluster that was different. The risk factors identified were low birth weight, prematurity, prolonged respiratory therapy, prolonged use of antibiotics, and maternal infection prior to delivery. Overcrowding and understaffing were recorded simultaneously with the clusters.

CONCLUSIONS

PFGE analysis showed three independent clusters. Several factors contributed to spread of the epidemic strains: (1) there were many severely premature and susceptible neonates, (2) the NICU was overcrowded during the clusters, and (3) transmission was likely to occur via the hands of staff. Cohorting and improvement of routine infection control measures led to the cessation of each cluster.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Finland

Data on methicillin-resistant Staphylococcus aureus (MRSA) cases notified to the National Infectious Disease Register (NIDR) and antibiotic resistance profiles of MRSA isolates sent to the national reference laboratory between 1997 and 2002 were analysed. In addition, the diagnostic methods used for MRSA identification in Finnish microbiology laboratories, the number of MRSA screening specimens studied, and the MRSA situation in long-term care facilities in 2001 were reviewed. MRSA cases notified to the NIDR rose from 120 in 1997 to 597 in 2002 (from 2.3 to 11.5 cases per 100,000 population). The increase was greatest in elderly people and outside Helsinki metropolitan area, in the districts where the proportion of non-multiresistant strains was most prominent. The National Committee for Clinical Laboratory Standard's guidelines for the oxacillin disk diffusion test were followed, except for the incubation temperature and time, which may have hindered detection of some MRSA strains. There was a wide geographic variation in the rates of MRSA, but this was not related to screening activity. MRSA isolates from long-term facilities accounted for more than half of the notifications to the NIDR in 2001.

Harmonization of pulsed-field gel electrophoresis protocols for epidemiological typing of strains of methicillin-resistant Staphylococcus aureus: a single approach developed by consensus in 10 European laboratories and its application for tracing the spread of related strains

Pulsed-fieldgel electrophoresis (PFGE) is the most common genotypic method used in reference and clinical laboratories for typing methicillin-resistant Staphylococcus aureus (MRSA). Many different protocols have been developed in laboratories that have extensive experience with the technique and have established national databases. However, the comparabilities of the different European PFGE protocols for MRSA and of the various national MRSA clones themselves had not been addressed until now. This multinational European Union (EU) project has established for the first time a European database of representative epidemic MRSA (EMRSA) strains and has compared them by using a new "harmonized" PFGE protocol developed by a consensus approach that has demonstrated sufficient reproducibility to allow the successful comparison of pulsed-field gels between laboratories and the tracking of strains around the EU. In-house protocols from 10 laboratories in eight European countries were compared by each center with a "gold standard" or initial harmonized protocol in which many of the parameters had been standardized. The group found that it was not important to standardize some elements of the protocol, such as the type of agarose, DNA block preparation, and plug digestion. Other elements were shown to be critical, namely, a standard gel volume and concentration of agarose, the DNA concentration in the plug, the ionic strength and volume of running buffer used, the running temperature, the voltage, and the switching times of electrophoresis. A new harmonized protocol was agreed on, further modified in a pilot study in two laboratories, and finally tested by all others. Seven laboratories' gels were found to be of sufficiently good quality to allow comparison of the strains by using a computer software program, while two gels could not be analyzed because of inadequate destaining and DNA overloading. Good-quality gels and inclusion of an internal quality control strain are essential before attempting intercenter PFGE comparisons. A number of clonally related strains have been shown to be present in multiple countries throughout Europe. The well-known Iberian clone has been demonstrated in Belgium, Finland, France, Germany, and Spain (and from the wider HARMONY collection in Portugal, Slovenia, and Sweden). Strains from the United Kingdom (EMRSA-15 and -16) have been identified in several othercountries, and other clonally related strains have also been identified. This highlights the need for closer international collaboration to monitor the spread of current epidemic strains as well as the emergence of new ones.

Serology and genetics of the flagellar antigen of Escherichia coli O157:H7a,7c

Among Escherichia coli strains of the O55:H7 serovar, which is considered the ancestor of Shiga toxin-producing E. coli (STEC) O157:H7, two subtypes, H7a,7b and H7a,7c (briefly, H7a,b and H7a,c, respectively), of the H7 flagellar antigen have been described previously [J. Wright and R. Villanueva, J. Hyg. (Camb.) 51:39-48, 1953; Y. A. Ratiner and V. A. Sinelnikova, Zh. Microbiol. Epidemiol. Immunobiol. 3:111-116, 1969). We have now studied 13 STEC O157:H7 strains and 1 O55:H7 strain that were epidemiologically unrelated, that originated from six countries on two continents, and that had different profiles when analyzed by multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and PCR for stx and eae. They were all found to possess the H7a,c flagellar antigen. Serum cross-absorption assays confirmed that their H antigens were indistinguishable from each other and from that of E. coli O55:H7a,c but differed from the standard H7a,b antigen of E. coli H test strain U5/41. It was shown by phage-mediated transduction that the flagellin genes for these two H-antigen subserotypes were alleles of the E. coli fliC locus. On the basis of the serological data obtained in this study and the molecular characteristics of E. coli fliC(H7) alleles recently published, it is inferred that H7a,c and H7a,b are the main serological subtypes of the group of E. coli H7 flagellins.

Elimination of epidemic methicillin-resistant Staphylococcus aureus from a university hospital and district institutions, Finland

From August 1991 to October 1992, two successive outbreaks of methicillin-resistant Staphylococcus aureus (MRSA) occurred at a hospital in Finland. During and after these outbreaks, MRSA was diagnosed in 202 persons in our medical district; >100 cases involved epidemic MRSA. When control policies failed to stop the epidemic, more aggressive measures were taken, including continuous staff education, contact isolation for MRSA-positive patients, systematic screening for persons exposed to MRSA, cohort nursing of MRSA-positive and MRSA-exposed patients in epidemic situations, and perception of the 30 medical institutions in that district as one epidemiologic entity brought under surveillance and control of the infection control team of Turku University Hospital. Two major epidemic strains, as well as eight additional strains, were eliminated; we were also able to prevent nosocomial spread of other MRSA strains. Our data show that controlling MRSA is possible if strict measures are taken before the organism becomes endemic. Similar control policies may be successful for dealing with new strains of multiresistant bacteria, such as vancomycin-resistant strains of S. aureus.

Community-acquired methicillin-resistant Staphylococcus aureus, Finland

Methicillin-resistant Staphylococcus aureus (MRSA) is no longer only hospital acquired. MRSA is defined as community acquired if the MRSA-positive specimen was obtained outside hospital settings or within 2 days of hospital admission, and if it was from a person who had not been hospitalized within 2 years before the date of MRSA isolation. To estimate the proportion of community-acquired MRSA, we analyzed previous hospitalizations for all MRSA-positive persons in Finland from 1997 to 1999 by using data from the National Hospital Discharge Register. Of 526 MRSA-positive persons, 21% had community-acquired MRSA. Three MRSA strains identified by phage typing, pulsed-field gel electrophoresis, and ribotyping were associated with community acquisition. None of the strains were multiresistant, and all showed an mec hypervariable region hybridization pattern A (HVR type A). None of the epidemic multiresistant hospital strains were prevalent in nonhospitalized persons. Our population-based data suggest that community-acquired MRSA may also arise de novo, through horizontal acquisition of the mecA gene.

Recognition of two groups of methicillin-resistant Staphylococcus aureus strains based on epidemiology, antimicrobial susceptibility, hypervariable-region type, and ribotype in Finland

Epidemiological evidence suggests that some methicillin-resistant Staphylococcus aureus (MRSA) strains are more prone to dissemination than others. We studied 72 MRSA strains, collected through nationwide MRSA surveillance in 1992 through 1999 and known to be either (i) sporadic, (ii) local outbreak strains spread within one hospital, or (iii) epidemic strains spread among hospitals, by antimicrobial susceptibility testing, hybridization of the mec hypervariable region (HVR), and ribotyping. Our results show that two main groups can be identified among these strains. The first group includes mainly nonepidemic, nonmultiresistant MRSA strains showing a specific mec HVR hybridization pattern, A, in combination with a variety of ribotypes. The other group includes multiresistant strains with mec HVR hybridization pattern B or C in association with closely related ribotype a or b. Sixty-four percent (9 of 14) of Finnish epidemic MRSA strains belong to the latter group. These findings support the existence of differences in epidemic potential among MRSA strains.

Eradication of methicillin-resistant Staphylococcus aureus from a health center ward and associated nursing home

BACKGROUND

Long-term health care facilities have been recognized as reservoirs of multiresistant bacterial strains, especially methicillin-resistant Staphylococcus aureus (MRSA). Efforts to control MRSA in this setting usually have been only partially effective. We describe herein the eradication of epidemic MRSA from a Finnish health care center ward and affiliated nursing home.

METHODS

The methods to control MRSA included (1) contact isolation precautions, (2) screening for asymptomatic carriage, (3) eradication of carriage, and (4) education of staff on hygienic measures. The first 6 patients with MRSA-positive findings were referred without delay to the Infectious Diseases Unit of the adjacent university hospital for eradication treatment. Later, an isolation unit of 6 rooms was founded in the health care center, where the MRSA-colonized patients were nursed as a separate cohort until they, in succession, were referred to the Infectious Diseases Unit for decolonization.

RESULTS

From May 20 through August 17, 1993, the epidemic MRSA strain was isolated from 8 long-term patients on the 40-bed ward of the health care center, 4 of the 59 residents of the nursing home, and 1 member of the staff. Eradication of carriage was successful in all except 1 patient with dementia, who was nursed in contact isolation in the health care center until his death 21 months later.

CONCLUSIONS

It is possible to eradicate MRSA from a long-term health care facility even after 13 cases by applying strict control measures. Our experience may be valuable in the future decision-making process for control of new and more challenging multiresistant bacteria, eg, vancomycin-resistant strains of MRSA.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Finland

This study reports the recent trends in the occurrence of methicillin-resistant Staphylococcus aureus in Finland, with special focus on characterization of the strains linked to interhospital epidemics and local outbreaks. Between 1981 and 1997, the annual number of methicillin-resistant Staphylococcus aureus isolations ranged from 89 to 272. Of all blood isolates of Staphylococcus aureus reported to the National Infectious Disease Register during the period 1995-97 (n = 2049), only six were resistant to methicillin. Between 1992 and 1997, typing analysis by various methods (i.e., antibiogram, phage typing, ribotyping, and pulsed-field gel electrophoresis) identified 18 different strains capable of causing intrahospital outbreaks or interhospital epidemics. These 18 strains were separated into 13 different ribotypes and 14 major pulsed-field gel electrophoresis types. Multiresistance was investigated as a possible marker for epidemicity. Eight of the ten interhospitally spread strains were multiresistant compared to only three of the eight intrahospitally spread outbreak strains. More than one-third of the epidemic and local outbreak strains were suspected to be of foreign origin. The majority (6 of 10) of the epidemics were localized in southern and western Finland, and the largest epidemic, which occurred in the Helsinki metropolitan area, involved over 200 persons. Thus far, the epidemics have remained primarily intracity problems, and only two strains have become endemic.

vanA and vanB incorporate into an endemic ampicillin-resistant vancomycin-sensitive Enterococcus faecium strain: effect on interpretation of clonality

Clonal spread and horizontal transfer in the spread of vancomycin resistance genes were investigated. Multiplex PCR, pulsed-field gel electrophoresis (PFGE), hybridization of enterococcal plasmids with the vanA and vanB probes, and sequencing of a fragment of vanB were used in the analysis. Before May 1996, 12 vancomycin-resistant Enterococcus faecium (VRE) isolates were found in Finland. Between May 1996 and October 1997, 156 VRE isolates were found in the Helsinki area. Between December 1997 and April 1998, fecal samples from 359 patients were cultured for VRE. One new case of colonization with VRE was found. During the outbreak period, 88% (137 of 155) of the VRE isolates belonged to two strains (VRE types I and II), as determined by PFGE. Each VRE type I isolate possessed vanB, and five isolates also had vanA. Of the 34 VRE type II isolates, 27 possessed vanA and 7 possessed vanB. Fifteen of 21 (71%) ampicillin-resistant, vancomycin-sensitive E. faecium (VSE) isolates found during and after the outbreak period in one ward were also of type II. Two VSE type II isolates were found in the hospital before the outbreak in 1995. By PFGE, the three groups (vanA, vanB, or no van gene) of type II shared the same band differences with the main type of VRE type II with vanA. None of the differences was specific to or determinative for any of the groups. Our material suggests that vanA and vanB incorporate into an endemic ampicillin-resistant VSE strain.

Assessment of resolution and intercenter reproducibility of results of genotyping Staphylococcus aureus by pulsed-field gel electrophoresis of SmaI macrorestriction fragments: a multicenter study

Twenty well-characterized isolates of methicillin-resistant Staphylococcus aureus were used to study the optimal resolution and interlaboratory reproducibility of pulsed-field gel electrophoresis (PFGE) of DNA macrorestriction fragments. Five identical isolates (one PFGE type), 5 isolates that produced related PFGE subtypes, and 10 isolates with unique PFGE patterns were analyzed blindly in 12 different laboratories by in-house protocols. In several laboratories a standardized PFGE protocol with a commercial kit was applied successfully as well. Eight of the centers correctly identified the genetic homogeneity of the identical isolates by both the in-house and standard protocols. Four of 12 laboratories failed to produce interpretable data by the standardized protocol, due to technical problems (primarily plug preparation). With the five related isolates, five of eight participants identified the same subtype interrelationships with both in-house and standard protocols. However, two participants identified multiple strain types in this group or classified some of the isolates as unrelated isolates rather than as subtypes. The remaining laboratory failed to distinguish differences between some of the related isolates by utilizing both the in-house and standardized protocols. There were large differences in the relative genome lengths of the isolates as calculated on the basis of the gel pictures. By visual inspection, the numbers of restriction fragments and overall banding pattern similarity in the three groups of isolates showed interlaboratory concordance, but centralized computer analysis of data from four laboratories yielded percent similarity values of only 85% for the group of identical isolates. The differences between the data sets obtained with in-house and standardized protocols could be the experimental parameters which differed with respect to the brand of equipment used, imaging software, running time (20 to 48 h), and pulsing conditions. In conclusion, it appears that the standardization of PFGE depends on controlling a variety of experimental intricacies, as is the case with other bacterial typing procedures.

Phylogenetic characterization and proposal of a new pigmented species to the genus Prevotella: Prevotella pallens sp. nov

Complete 16S rRNA gene sequences of three representative strains of anaerobic, Gram-negative, pigmented, moderately saccharolytic, indole-positive bacteria isolated from the oral cavity of humans were determined. According to comparative analyses of the rRNA sequence data, this organism represents a previously unknown species within the genus Prevotella. In addition, 22 representative strains and 21 reference strains (including 11 Prevotella intermedia and 10 Prevotella nigrescens strains) were subjected to multilocus enzyme electrophoretic analysis. The strains were consistently separated into three clearly distinct groups, corresponding to their previous entities. On the basis of the present phylogenetic results that confirmed our biochemical and genetic data, we propose a new species, Prevotella pallens. The type strain is NCTC 13042 (= AHN 10371).