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Published :30 November 2007, Volume 1, No 48 (PDF file, 242 KB)

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Staphylococcus aureus with Panton-Valentine Leucocidin from England and Wales: 2005-6

Panton-Valentine Leukocidin (PVL) is a toxin which destroys white blood cells and is carried by less than 2% of clinical isolates of Staphylococcus aureus . PVL can be detected in both meticillin-sensitive S. aureus (MSSA) and meticillin resistant S. aureus (MRSA). The majority of isolates causing infection in the UK have been MSSA. Community-associated MRSA (CA-MRSA) are more likely to produce PVL than hospital-associated MRSA. PVL-positive S. aureus are normally associated with necrotising pyogenic cutaneous infections and occasionally with cellulitis or tissue necrosis. They can rarely cause other severe invasive infections such as septic arthritis, bacteraemia, purpura fulminans, or community-acquired necrotising pneumonia.

From 2005 to 2006 the HPA Staphylococcus Reference Laboratory (SRL) enhanced its monitoring of PVL-SA to help ascertain the burden of PVL related disease. Four hundred and ninety-six cases of PVL- S. aureus (SA) were identified in 2006 representing a two-fold increase from the 224 identified in 2005. The number of cases of PVL-MRSA rose from 117 to 159 year-on-year, the remainder being PVL-MSSA. The isolates included strains associated with outbreaks of PVL-related disease in both the community and healthcare settings. The majority of PVL-SA were from individuals who had relatively mild skin and soft tissue infections.

It is not clear if the increased numbers of PVL-SA reflect improved case ascertainment of PVL-related syndromes and/or an increasing prevalence of PVL-SA. Further systematic surveillance-based studies are planned to address this.

 

 

 

 

 

 

 

 

Review of risks from tritium

 

 

The independent Advisory Group on Ionising Radiation has published a report reviewing the risks of exposure to tritium, a radioactive isotope of hydrogen [1]. Tritium is used in scientific and medical research and it also has various industrial applications. Following an extensive review of scientific evidence on the risks from exposure to tritium, the Advisory Group suggests that the International Commission on Radiological Protection (ICRP) should consider increasing its radiation weighting factor for tritium from 1 to 2. Radiation weighting factors are used to calculate doses and risks from radiation exposures.

Tritium is a radioactive isotope of hydrogen that decays by beta emissions with a maximum energy of 15.6 keV and a half-life of 12.3 years. It is formed through several processes, both natural and artificial, including nuclear fission and fusion power generation.

The Advisory Group has examined biological evidence from published laboratory experiments with tritium in cell cultures (in vitro) and from animal experiments (in vivo). They have also reviewed the published evidence for effects on human health (epidemiology). The evidence indicates that tritium has a larger impact on biological systems than gamma rays or x-rays and its relative biological effectiveness (RBE) is greater than 1. This is the basis for the Advisory Group's recommendation that the RBE value for tritium should be taken as 2 and its suggestion that ICRP should consider increasing its radiation weighting factor for tritium from 1 to 2.

Epidemiological data on risks associated with tritium exposure are not strong because most of the studies conducted worldwide involved small numbers of people. The report therefore recommends that consideration is given to an international collaborative epidemiological study of tritium exposed populations.

In reviewing biokinetic models for tritium the report notes a wide range of animal and human data support the current ICRP models for radiation exposure and that models for tritiated compounds are under development. The report concludes by welcoming the development of new tritium models by ICRP and recommends that they be adopted for routine dose assessments when available.

References
1. Review of Risks from Tritium. Report of the Independent Advisory Group on Ionising Radiation. Documents of the Health Protection Agency. Chilton: Health Protection Agency, November 2007. ISBN: 978-0-85951-610-5. Available at: http://www.hpa.org.uk/publications/PublicationDisplay.asp?PublicationID=0

Printed copy, £20.00 + 10% postage and packing, available from CRCE Information Office (Tel: 01235 822742/822603, email: chiltoninformationoffice@hpa.org.uk).

Consultation: Interferon Gamma Release Assay (IGRA) tests for tuberculosis (TB): position statement and Q&As for healthcare professionals and the public

The Health Protection Agency Tuberculosis (TB) Programme Board has drafted a position statement on the use of Interferon Gamma Release Assay (IGRA) tests for TB. The TB Programme Board has also developed a set of Questions and Answers (Q&As) on IGRA testing for the diagnosis of Mycobacterium tuberculosis infection . A consultation on these documents is currently underway on the HPA website at http://www.hpa.org.uk/consultations/2007/IGRA.htm.

Stakeholders are invited to comment on these provisional recommendations via the website.
The consultation deadline is 23 December 2007.

If individuals wish to comment they shoul contact the stakeholder organisation that most closely represents their interests and pass comments to them. Further information on the consultation is available at http://www.hpa.org.uk/consultations/2007/IGRA.htm.

 

Unusual illness guidelines – new content on the HPA Deliberate and Accidental Release web pages

The fully revised and update version of the Initial Investigation and Management of Outbreaks and Incidents of Unusual Illnesses – A Guide for Health Professionals version 4.0, 19 November 2007 is now available at: http://www.hpa.org.uk/infections/topics_az/deliberate_release/Unknown/unusual_illnesses.htm

Sub-documents for specialist professions, extracted from the full document, are also available for each of the following:

  • Ambulance service

  • Hospital clinicians, including Emergency Departments

  • General Practitioners

  • Occupational Health Services

  • Histopathologists and Anatomical Pathology Technologists

  • Local laboratories

  • Public Health professionals

The document is intended as an aid to decision making for health professionals and other health protection personnel who may be involved in the initial investigation, management and response to cases of unusual illness.

Unusual illness incidents may present as single or multiple cases of unexplained disease or syndrome with atypical signs or symptoms especially if accompanied by high morbidity or mortality. Outbreaks and incidents of unusual illnesses might have any one of a number of causes, including infectious, chemical, or radiological. The aetiological agent may remain undetermined, and there is also the possibility of new and emerging conditions.

Although the document cannot cover all possible eventualities, it is vital that those involved are confident about initial decisions and actions as prompt appropriate actions are likely to be crucial.

Please send comments on the document or web pages to DrComments@hpa.org.uk