For bacterial typing to be useful, the development, validation and appropriate application of typing methods must follow unified criteria. Over a decade ago, ESGEM, the ESCMID (Europen Society for ...Clinical Microbiology and Infectious Diseases) Study Group on Epidemiological Markers, produced guidelines for optimal use and quality assessment of the then most frequently used typing procedures. We present here an update of these guidelines, taking into account the spectacular increase in the number and quality of typing methods made available over the past decade. Newer and older, phenotypic and genotypic methods for typing of all clinically relevant bacterial species are described according to their principles, advantages and disadvantages. Criteria for their evaluation and application and the interpretation of their results are proposed. Finally, the issues of reporting, standardisation, quality assessment and international networks are discussed. It must be emphasised that typing results can never stand alone and need to be interpreted in the context of all available epidemiological, clinical and demographical data relating to the infectious disease under investigation. A strategic effort on the part of all workers in the field is thus mandatory to combat emerging infectious diseases, as is financial support from national and international granting bodies and health authorities.
The usefulness of spa typing was evaluated in relation to pulsed-field gel electrophoresis (PFGE), as a tool for epidemiological typing of methicillin-resistant Staphylococcus aureus (MRSA) in a ...low-prevalence region in southern Sweden. Bacterial isolates from 216 MRSA cases, newly identified in 2000–2004, were studied. The isolates were obtained from infected patients (31%), and from colonized individuals found by screening (69%). In total, 49 spa types and 73 PFGE patterns were identified. The discriminatory power of spa typing was lower (94.9 ± 1.8%) than that of PFGE (97.3 ± 1.2%). For two spa types (t002 and t008) the Panton–Valentine leukocidin results added useful discriminatory information. The most common spa types were t044 (n = 31; four PFGE patterns), t002 (n = 24; 10 PFGE patterns), t067 (n = 12; four PFGE patterns), t050 (n = 12; one PFGE pattern), and t324 (n = 11; one PFGE pattern). Epidemiological investigations identified 91 single cases and 39 transmission chains, each involving two to 13 cases. All the transmission chains were held together both by spa and PFGE typing. Among the 91 single-case isolates, 33 spa types and 50 PFGE patterns were unique (matchless) at the time of identification. The low prevalence of MRSA, the low number of outbreaks, and the wide spectrum of strains due to frequent acquisitions abroad (49% of the cases), makes spa typing a useful complement to epidemiological investigations in our setting. However, we still recommend the continued use of PFGE for further discrimination of isolates with identical spa types when epidemiological data can not exclude possible transmission.
Fast and reliable epidemiological typing methods for identifying outbreaks and epidemic strains of extended spectrum β-lactamase (ESBL) producing
Enterobacteriaceae are urgently needed. The ...DiversiLab system (DL) has been proposed for these purposes. We compared DL to pulsed-field gel electrophoresis (PFGE) on a national collection of ESBL-producing
Escherichia coli (n
=
258; of which 226 isolates were typeable with PFGE) and
Klebsiella pneumoniae (n
=
48) isolated in 2007. For
E. coli the Wallace coefficients showed that the probability of two isolates of the same DL type having the same PFGE type was only 19.8% and the probability of two isolates of the same PFGE type having the same DL type was 90.4%. For
K. pneumoniae the Wallace coefficients showed that the probability of two isolates of the same DL type having the same PFGE type was 100% and the probability of two isolates of the same PFGE type having the same DL type was 79%, indicating that for this
K. pneumoniae strain collection DL was slightly more discriminatory. Only four of 48 isolates had discordant results with the two methods. In
E. coli 42% of the isolates were sequence type 131 and these isolates were related at >
95% similarity with DL and at ≥
60% similarity with PFGE. In summary, for
E. coli DL performed well in identifying isolates related by PFGE, but overestimated the genetic relatedness in the studied collection. This indicates that DL could be a primary screening method for excluding unrelated isolates. Isolates shown to be related must be confirmed with a more discriminatory method. For
K. pneumoniae, DL discriminated well but overestimated the diversity of the isolates compared to PFGE, assuming a risk of missing possible genetic relatedness.
Countries such as Sweden that have a low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) offer the opportunity to discern and study transmission of imported cases of MRSA. We ...analyzed 444 imported cases of MRSA acquisition reported in Sweden during 2000-2003. Risk for MRSA in returning travelers ranged from 0.1 (95% confidence interval CI 0.01-0.4) per 1 million travelers to Nordic countries to 59.4 (95% CI 44.5-79.3) per 1 million travelers to North Africa and the Middle East. Most imported cases (246, 55%) were healthcare acquired, but regions with the highest risk for MRSA in travelers showed a correlation with community acquisition (r = 0.81, p = 0.001). Characteristic differences in MRSA strains acquired were dependent on the region from which they originated and whether they were community or healthcare acquired. Knowledge of differences in transmission of MRSA may improve control measures against imported cases.
Surveillance of communicable diseases is a public health corner stone. Routine notification data on communicable diseases are used as a basis for public health action as well as for policy making. ...While there are agreed standards for evaluating the performance of surveillance systems, it is rarely possible to analyse the validity of the data entered into these systems. In this study we compared data on all Swedish cases of methicillin-resistant Staphylococcus aureus (MRSA) routinely notified between 2000 and 2003 with follow-up information collected for each of these cases as part of a public health project. The variables Reason for testing (clinical sample, contact tracing, screening of risk group), Clinical presentation (disease, colonisation), Transmission setting (healthcare-acquired, community-acquired), Country of acquisition (Sweden, abroad) and Risk-occupation (yes, no) were analysed for sensitivity, positive predictive value and completeness of answers. The sensitivity varied between 23% and 83%, the positive predictive values were generally higher (55% to 97%), while missing answers varied from 11% to 59%. The proportion of community-acquired cases was markedly higher when excluding either cases of MRSA colonisation or cases found through public health-initiated activities (contact tracing or screening of risk groups). We conclude that the quality of routine surveillance data may be inadequate for in-depth epidemiological analyses. This should be taken into account when interpreting routine surveillance figures. Whether or not the case definition includes cases of MRSA colonisation may have a significant impact on population-wide estimates of MRSA occurrence.
Infections by community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) have been reported worldwide. Here we present characterisation of the first CA-MRSA isolated in Latvia. A ...PVL-positive ST30-MRSA-IV strain was isolated from a nasal swab and the central venous catheter of a patient with fever and multiple organ failure. The PFGE pattern of this strain was identical to pattern SE00-3 of MRSA isolated in Sweden from 29 patients during 2000-2003. This strain is related to the South Pacific area, and its appearance in Sweden and Latvia demonstrates its global spread.
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