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Volume 2 No 33; 15 August 2008

 

S. Agona PT39: increase in new salmonella strain in UK and Ireland – an update

Investigation of an outbreak of Salmonella Agona PT 39 infections that has so far affected England and Wales, Scotland, Northern Ireland, the Republic of Ireland [1] and Finland is continuing.

As of Thursday 14 August, a total of 119 cases had been identified, all having the same Pulse Field Gel Electrophoresis (PFGE) profile designated as SAGOXB.0066, of which 77 were in England, Wales and Northern Ireland. Of the 119 cases, 110 are confirmed with the remaining nine awaiting definitive analysis. The most recent date of onset reported is 29 July 2008. Cases range in age from three months to 79 years with a median age of 27 years. The three-month-old infant is a secondary case. Most of the cases are males (56%; ratio is 67 male cases to 53 female cases). To date, 14 cases are known to have been or are currently hospitalised. There has been one death associated with the outbreak, an elderly female patient in the UK who contracted S. Agona whilst an inpatient and subsequently died. The cause of death is reported as ischaemic colitis secondary to salmonella infection.

Microbiological investigations have demonstrated S. Agona isolates with the identical PFGE profile SAGOXB.0066, in cases and in food samples from a particular factory in the Republic of Ireland and from outlets supplied by that factory. Interviews of cases indicate that food products from that company may be related to some of these cases: some had eaten sandwiches containing one of the products from the company in question. A case control study is underway to test the hypotheses that cases are more likely to have eaten at outlets supplied by the company in question and/or foods supplied by it.

Production has stopped at the implicated part of the factory that is a focus of concern. Product re-calls of selected batches of cooked beef, cooked chicken and cooked bacon products have also taken place. The company has an extensive product distribution list that covers distribution to the UK, Republic of Ireland and many European countries. A confirmed case in Finland has eaten food from a branch of the retail outlet chain implicated in Ireland and the UK. A Rapid Alert System for Food and Feed (RASFF) was released on 4 August, and updated on 8 and 11 August, by the Food Safety Authority of Ireland. An up-to-date list of the products recalled is available on the Food Safety Authority of Ireland's website (http://www.fsai.ie/).

The outbreak investigation is being managed by a multinational outbreak control team comprising experts from the following organisations: the Health Protection Surveillance Centre (HPSC), Ireland; the National Salmonella Reference Laboratory (NSRL), Ireland; the Health Protection Scotland (HPS); the National Public Health Service for Wales (NPHS); the Health Protection Agency Centre for Infections, London; the Food Safety Authority of Ireland (FSAI); the Food Standards Agency (FSA), London; and the Department of Agriculture Fisheries and Food (DAFF), Ireland.

The multinational outbreak control team has published a preliminary report on the investigation in Eurosurveillance [2].

References

1. HPA. Salmonella Agona PT39: increase in new salmonella strain in UK and Ireland. Health Protection Report [serial online] 2008; 1 August 2008, 2(31): news. Available at http://www.hpa.org.uk/hpr/archives/2008/hpr3108.pdf

2. O'Flanagan D, Cormican M, McKeown P, Nicolay N, et al. A multi-country outbreak of Salmonella Agona, February-August 2008. Euro Surveill. 2008;13(33):pii=18956. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=18956.

Accelerated publication schedule for MRSA bacteraemia data

Mandatory MRSA bacteraemia data is to be published according to an accelerated schedule for the April-June data (Quarter 1) onwards. The accelerated schedule has been introduced in response to a request from the Department of Health (DH) and in recognition of the keen public interest in mandatory healthcare associated infection data, and particular interest from the NHS, as well as from other stakeholders, in the April-June quarter for 2008/09, which is the target quarter for achievement of the Government’s targetted reduction in the number of MRSA bacteraemia infections by 50%. The April-June 2008 quarter mandatory MRSA bacteraemia data will be published on 18 September instead of in October as previously indicated.

The HPA and DH have been working for some time towards earlier publication of mandatory MRSA bacteraemia and C. difficile data. The intention had been that, from the fourth quarter of 2008/09, both the MRSA bacteraemia and the C. difficile quarterly data would be published according to an accelerated schedule. It is not possible to bring this accelerated schedule forward for the C. difficile data because of the greater complexity of the outputs (which will include Primary Care Organisation outputs). However, in view of the smaller data set and less complex analyses, and in view of the public interest in the data for the first quarter of 2008/09 in particular, DH has requested and the HPA has agreed that the release of the 2008-09 Q1 MRSA bacteraemia mandatory surveillance data, and the subsequent quarterly releases of MRSA bacteraemia mandatory data, should be brought forward to allow these figures to be in the public domain as soon as possible. It has been agreed by the statistical and epidemiological teams in DH and HPA, respectively, that a shorter validation period should still produce figures within existing standards of tolerance for accuracy. As previously, some changes to figures may occur as a result of retrospective validation, and these will be published in subsequent quarters.

Since the mandatory healthcare reporting system was introduced, the number of changes in MRSA bacteraemia figures due to validation processes has decreased. Analysis by statisticians and epidemiologists in DH and HPA indicate that moving to an accelerated schedule, with a shorter period of validation, would not be likely to result in a significant change in accuracy, while speeding up the data publication process. In implementing such an accelerated schedule, HPA would continue to undertake the validation processes after publication to investigate any discrepancies, eg reconciliation with routine laboratory reports.

The accelerated schedule of publication of mandatory MRSA bacteraemia data will apply for all subsequent quarters of 2008/09, with a view to introducing a similar accelerated schedule for the publication of mandatory C. difficile data from the fourth quarter of 2008/09, thereby bringing the publication of both data sets back together. The revised publication schedule presented below will also be reflected in the statistics publication plan on the DH website (http://www.dh.gov.uk/en/Publicationsandstatistics/Statistics/CodeOfPractice/DH_4016423).

The forward publication schedule for MRSA bacteraemia and C. difficile will be as follows:

April-June 2008 data
MRSA: 18 September
C. difficile: 23 October.

July-September 2008 data
MRSA: 18 December
C. difficile: 15 January.

October-December 2008 data
MRSA: 19 March
C. difficile: 16 April.

Diagnosis and management of PVL-SA infections in England and Wales – an update

Following publication of a draft for public consultation in January this year, the HPA has published the final version of new guidance on the diagnosis and management of Panton-Valentine leukocidin-associated Staphylococcus aureus (PVL-SA) infections [1], replacing interim guidance published two years ago.

Studies have shown that fewer than 2% of S. aureus isolates referred to the HPA Staphylococcus Reference Unit have been PVL-positive [2], including both meticillin-resistant and -sensitive strains (MRSA and MSSA). These PVL-SA strains most commonly cause skin and soft tissue infections, particularly boils and abscesses. More rarely, they can cause serious illness such as pneumonia, septic arthritis or bacteraemia in otherwise healthy young people.

The HPA has called for vigilance among health protection specialists in the health service, and for awareness of the problem among possible “risk groups” and “risk environments”, as a means of reducing the risk of spread of PVL-SA infections when they do occur.

The guidance encompasses microbiological testing and screening, and case management, information for healthcare workers in primary care, for GPs and for other healthcare workers in the community, such as occupational health departments. It also reiterates conventional day-to-day personal hygiene advice relevant to people, whether health specialists or not, working in closed communities. North American experience suggests there is high risk of infected or colonised individuals transmitting PVL-SA in such settings as: households, schools, close contact sports (wrestling, American football, rugby, etc), military training camps, gyms and prisons.

In these settings, the US Centers for Disease Control has suggested, the focus of precautionary measures should be the "Five C's", ie: 1) Contaminated items; 2) Close contact 3) Crowding 4) Cleanliness, and 5) Cuts and other compromised skin integrity.

The guidance notes that PVL-SA have been recognised for more than a century as a cause of skin and soft tissue infections. For example, in the 1950s and 1960s in the UK and abroad, one PVL-MSSA strain spread widely among healthy people in the community as well as in hospitalised patients and healthcare workers. More recently, a major problem has emerged with PVL-producing community-associated MRSA in North America, one strain in particular (the USA300 clone) spreading widely in US hospitals [3]. Why some newly recognized PVL-MRSA strains appear so transmissible and associated with an escalating morbidity and mortality is the subject of intense investigation.

The guidance is primarily concerned with management of infections once detected and encompasses:
• Microbiological testing and screening in cases of suspected outbreaks;
• Management of cases;
• Decolonization and screening of patients and their close contacts;
• Infection prevention and control in hospitals and the community; and
• Surveillance.

It concludes with appendices providing general information for patients and guidance on:
• procedures for decolonization, practical measures for reducing the spread of PVL-SA in communal and recreational settings, schools and nurseries;
• advice for managers of care homes;
• advice for those responsible for screening and treatment in primary care settings; and
• special considerations applying in the case of infections in children.

In the light of the evolving situation in other countries, there have been national alerts and improved case ascertainment initiatives to raise the awareness of PVL-SA in England and Wales. The new guidance is an important element of these activities, providing healthcare professionals with easily accessible advice on the recognition, investigation and management of cases. It is based on expert opinion following review of the international literature and experience gained in the UK, Europe, the USA and Canada. However, as such, it is not entirely evidence-based since there is little evidence in the international literature for some of the control measures recommended, so it is anticipated that the guidance will be updated in the light of developing knowledge.

PVL-SA surveillance in England and Wales

The HPA has been monitoring PVL-related disease throughout England and Wales. During 2005 and 2006, a total of 720 cases of PVL-SA were identified from isolates referred to the HPA Staphylococcus Reference Unit for testing and characterization. Of these, 224 were in 2005 and 496 in 2006, representing a two-fold increase, possibly the result of increased awareness and reporting.

Provisional data for 2007 show 1361 PVL-SA were identified, representing a 2.7-fold increase over the 2006 figures (published in November 2007 [4]). Of the 1361, 845 (62%) were PVL-MSSA and 516 (38%) were PVL-MRSA.

What is not clear is whether the increase in PVL-SA is due to improved awareness and case recognition and/or pro-active close contact tracing, or whether it reflects a genuine increase in PVL-SA nationally.

Planned systematic surveillance-based studies will provide more robust data for monitoring trends and the Department of Health is funding a project through the HPA to investigate the prevalence of PVL-SA in the community.

References

1. HPA guidance on the diagnosis and management of PVL-associated Staphylococcus aureus infections - report prepared by the PVL sub-group of the Steering Group on Healthcare Associated Infection. Available at: http://www.hpa.org.uk/PVL-SA_FinalGuidance.pdf

2. Holmes A, Ganner M, McGuane S, Pitt TL, Cookson BD, Kearns AM. Staphylococcus aureus isolates carrying Panton-Valentine leucocidin genes in England and Wales: frequency, characterization, and association with clinical disease. J Clin Microbiol. 2005 May; 43(5): 2384-90.

3. Patel M, Waites KB, Hoesley CJ, Stamm AM, Canupp KC, Moser SA. Emergence of USA300 MRSA in a tertiary medical centre: implications for epidemiological studies. J Hosp Infect 2008; 68: 208-213.

4. Staphylococcus aureus with Panton-Valentine Leucocidin from England and Wales: 2005-6, Health Protection Report [serial online], 30 November 2007, 2(48): news. Available at http://www.hpa.org.uk/hpr/archives/2007/news2007/news4807.htm.

Further information

PVL-associated Staphylococcus aureus – Frequently Asked Questions (HPA website), http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1207208304710?p=1207208304710.
Ten tips on MRSA in primary care, Pulse, 2 May 2008. Available at http://www.pulsetoday.co.uk/story.asp?sectioncode=18&storycode=4118850.