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Volume 3 No 30; 31 July 2009

HPR Home | Archives | 2009 news

• Increase in cases of pregnancy-associated listeriosis in England and Wales
  
  
• Microbiological quality of ready-to-eat speciality meats from markets and specialist food outlets across the UK
  
  
• Pandemic flu: UK situation at 30 July 2009
  
  
• Synopsis of the method used to estimate the number of pandemic influenza (H1N1) 2009 cases in England in the week 21 to 27 July 2009
  

Increase in cases of pregnancy-associated listeriosis in England and Wales

The HPA Centre for infections has identified an increase in the reporting of pregnancy-related cases of listeriosis (ie where a mother and foetus/neonate are affected) in England and Wales. Of the 87 cases of Listeria monocytogenes infection reported between week 1 and week 30, 2009, 21% (n=18) were pregnancy-related compared to 12% (60/504) for the same period between 2004 and 2008 (chi-squared P=0.03). Cases were distributed across England and Wales, with more cases reported in London and the West Midlands in 2009 (table 1). Provisional 2008 live birth data suggest that incidence in these regions are higher than elsewhere (relative risk (RR) 2.99 [95% confidence intervals (CI) 1.04-8.62] and RR 3.55 [95%CI 1.07-11.78] respectively).

Table 1. Pregnancy-related cases of L. monocytogenes infection by region, weeks 1 to 30, 2004 to 2009

Region *	Cases by year
	2004	2005	2006	2007	2008	2009
E Mids	-	1	1	2	2	-
East	-	1	2	1	2	-
London	3	1	4	5	3	6
N East	-	2	1	2	-	1
N West	2	2	1	2	1	2
S East	-	1	2	-	-	1
S West	-	-	1	1	2	2
W Mids	-	2	1	1	1	4
Wales	2	-	-	-	-	1
York & Humb.	1	2	1	1	-	1

* Based on patient postcode and laboratory region as available.

Classification of ethnicity based on patient name indicated that 56% of the pregnancy-related cases reported in 2009 were from ethnic minorities, compared to 46% for the same period between 2004 and 2008, which does not represent a significant increase (chi-squared P=0.47). However, amongst pregnancy related cases, there has been a significant increasing trend in the proportion of cases from ethnic minorities between 2004 and 2009 (chi-squared P=0.03). Standardised epidemiological data from cases, available for a subset of cases since 2005, validated ethnicity based on patient name (positive predictive value for non-White British ethnicity 89.6% [95%CI 77.3-96.5%]; negative predictive value 90.1% [95%CI 85.5-93.6%]).

Microbiological characterisation data (serotyping and Amplified Fragment Length Polymorphism [AFLP] typing) were available for 15 pregnancy-related cases in 2009 and 47 cases between 2004 and 2008. Seven different subtypes have been reported in 2009 to date, suggesting that the increase is unlikely to be as a result of a point source outbreak. However, sero-aflp type 4b V accounted for 47% (n=7) of cases in 2009 compared to 34% of cases (n=16) between 2004 and 2008 (chi-squared P=0.38). Two other strains (4b XV and 1/2a XI), both of which have accounted for two cases in 2009, were not reported amongst pregnancy-related cases between 2004 and 2008.

While ethnic minorities and sero-aflp type 4b V are both over represented amongst the pregnancy related cases in 2009 to date, these factors do not fully explain the recent increase. It is likely that 2009 represents a continued trend in the emergence of pregnancy related listeriosis amongst women from ethnic minorities.

In order to investigate this increase further, microbiologists are urged to expedite the referral of all putative L. monocytogenes isolates to Dr Kathie Grant, Foodborne Pathogen Reference Unit, Health Protection Agency Centre for Infections (tel: 020 8327 6505/711) for confirmation and subtyping. Health Protection Unit staff should continue to send completed Listeria surveillance questionnaires (http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947370264), conducted where appropriate, to Dr Iain Gillespie, Health Protection Agency Centre for Infections (fax: 020 8327 7112).

Microbiological quality of ready-to-eat speciality meats from markets and specialist food outlets across the UK

A recent study carried out by the Health Protection Agency, the Local Authorities Co-ordinators of Regulatory Services (LACORS) and local councils [1], involving the sampling of over 2000 speciality meats (ie continental sausage, cured/fermented and dried meats) from markets and specialist food outlets, has shown that 99% were of satisfactory or acceptable microbiological quality [2]. However, 1% of speciality meats were found to be unacceptable on account of the presence of Salmonella or unsafe levels of Listeria monocytogenes.

This study concludes that the presence of pathogens, such as Salmonella and Listeria monocytogenes, in pre-packed ready-to-eat meats suggests that contamination occurred before the point of sale, either with incomplete elimination during processing or as a result of cross-contamination. The study emphasises the importance of ensuring products do not become contaminated before final packaging, that storage conditions are controlled, and that durability dates are an accurate indication of the shelf life of the product so as to minimise the potential for Listeria monocytogenes to be present at levels hazardous to health at the point of sale.

The survey was the largest study to have solely focused on speciality meats from markets and specialist retailers in the UK and followed a number of Salmonella contamination incidents reported to the HPA, linked to speciality meats sampled from travelling markets and specialist shops, that resulted in products being withdrawn from sale following action by the Food Standards Agency.

A total of 2359 ready-to-eat speciality meat products were collected from markets and specialist food shops by sampling officers from 257 environmental health departments, involving 50 local authority food liaison groups across England, Wales, Scotland and Northern Ireland. The samples were tested for Salmonella, Listeria monocytogenes, other Listeria species, Staphylococcus aureus, and E. coli.

References/notes

1. Gormley FJ, Little CL, Grant KA, de Pinna E, McLauchlin J, and the Food, Water and Environmental Surveillance Network, on behalf the Local Authorities Co-ordinators of Regulatory Services (LACORS) and the Health Protection Agency (HPA). Assessment of the microbiological safety of speciality meats from markets and small specialist retailers, with a focus on Salmonella spp. and Listeria monocytogenes. Downloadable from the HPA website at: http://www.hpa.org.uk/foodsampling.

2. The terms used to express the microbiological quality of ready-to-eat foods are: Satisfactory: test results indicating good microbiological quality; Acceptable: an index reflecting a borderline limit of microbiological quality; Unsatisfactory: test results indicating that further sampling may be necessary and that environmental health officers may wish to undertake a further inspection of the premises concerned to determine whether hygiene practices for food production or handling are adequate or not; Unacceptable/potentially hazardous: test results indicating that urgent attention is needed to locate the source of the problem; a detailed risk assessment is recommended. Such samples are potentially injurious to health and/or unfit for human consumption (contravening Article 14 (Food Safety Requirements) of Regulation (EC) No.178/2002, the General Food Law Regulation).

Pandemic flu: UK situation at 30 July 2009

The latest HPA Weekly Pandemic Flu Update [1] notes the following developments as at 30 July:

• GP consultation rates showed a plateau or small decrease over the previous week in England. This coincided with the start of school holidays and the introduction of the National Pandemic Flu Service;
• there was no sign that the virus was changing, becoming more severe or developing resistance to anti-virals. The small number of deaths have been mainly in older children and adults with underlying risk factors;
• overall, across the UK, indications were that the number of cases were no longer rising rapidly, and may have plateaued; and
• producing reliable estimates of new cases became more challenging following the introduction of the National Pandemic Flu Service (see following news item) and issues such as the start of the school holidays. On an equivalent basis to previous weeks, HPA estimated that there had been 110,000 new cases in England in the previous week (within a possible range of 60,000 to 160,000). The estimated number of cases in 5-14 year olds decreased. Estimated cases in other age-groups, and in the North, continued to increase.

A more detailed review of epidemiological data for the week-ending 26 July 2009 (week 31) is available at: www.hpa.org.uk/swineflu/surveillance&epidemiology [2].

References

1. Weekly pandemic flu update (30 July 2009), (HPA press release of 30 July 2009). HPA website: National Press Releases.

2. HPA Weekly National Influenza Report (30 July 2009, week 31), HPA website: Swine Flu / Surveillance and Epidemiology.

Synopsis of the method used to estimate the number of pandemic influenza (H1N1) 2009 cases in England in the week 21 to 27July 2009

The method currently used to obtain an estimate of the number of pandemic influenza (H1N1) 2009 cases relies on data from two surveillance systems: the QSurveillance® scheme, that provides an estimate of numbers consulting a GP with influenza-like illness (ILI); and the Royal College of General Practitioners (RCGP) and HPA Regional Microbiology Network scheme for swabbing clinically diagnosed cases.

The QSurveillance®-derived estimates of the daily number of people consulting their GP with a diagnosis of ILI are aggregated by age group (less than 1 year,1-4 years, 5-14years,15-24 years, 25-44 years, 45-64 years, 65 years and older), by Strategic Health Authority (SHA) and by week (Tuesday to Monday). The sum of the average size of the GP lists for these categories is also obtained from QSurveillance®.

In data from the RCGP/HPA scheme, swabs are classified as positive or negative for pandemic (H1N1) 2009 virus: these results are used as the dependent variable in a 'mixed-effects' logistic regression model. Due to the small number of swabs taken in certain SHAs, the SHAs have been grouped into 4 regions: London, West Midlands, North (North East, North West, Yorkshire & Humberside, and East Midlands), and South (East of England, South Central, South East Coast, and South West). From this model, the estimated positivity rates for swabs is obtained by region for the same weeks and age groups as used for ILI consultations from QSurveillance®.

The observed number of ILI consultations from QSurveillance® are multiplied by the estimated positivity rate in each of the SHAs, by age group categories for each week. These results are then scaled by the ratio of the 2007 ONS population estimates to the QSurveillance® population in each category. The resultant figures provide estimates of the numbers of pandemic (H1N1) 2009 cases in each week by SHA and age group that visit their GP.

There is currently no reliable information about the proportion of pandemic (H1N1) 2009 cases who consult their GP. It is thought, however, that this proportion is likely to lie within the range 0.2 (20%) to 0.5 (50%). This proportion is based on research demonstrating that approximately 10% of those with symptoms visit their GPs during normal flu seasons; and an assumption that this percentage is likely to be higher at present due to heightened awareness (and anxiety) about pandemic H1N1. Preliminary estimates from flusurvey, a system to monitor the activity of ILI in the population through the internet (www.flusurvey.co.uk), are within this range. These two extremes have been applied as scaling factors to the estimated numbers of pandemic (H1N1) 2009 cases who consult their GP to give a range within which the actual number of pandemic (H1N1) 2009 cases occurring in England that week is likely to fall.

The National Pandemic Flu Service (NPFS) became operational on 23 July and will undoubtedly have reduced the proportion of pandemic (H1N1) 2009 cases who consulted their GP within the week 21 July to 27 July. Again, there is no reliable information on how much the NPFS will reduce the proportion consulting their GP. However, under 1 year olds are not to be managed by NPFS and will continue to be referred to their GP. Therefore, for week 21 July to 27 July, an estimate of the reduction in the proportion consulted has been obtained from the relative increase in the estimated cases of pandemic (H1N1) 2009 in children under 1 compared to other age groups, excluding the 5 to 14 year olds and the over 65 year olds. These were not considered, as changes in cases could result from altered mixing patterns due to the close of schools for the summer holidays (5 to 14 year olds), and the higher incidence of risk factors likely to result in GP referral (over 65 year olds). There was a relative reduction of around 10% in these age groups compared to the under 1 year olds and this has been assumed to be attributable to the NPFS. Thus, the scaling factors of 2 (50% of cases visit their GP) and 5 (20% of cases visit their GP) were increased to 2.22 and 5.56, respectively, for those aged 1 or older and under 65 in the week 21 July to the 27 July.

The figure provided in the HPA weekly pandemic flu update (110,000) represents a mid-point around the two likely extremes of pandemic (H1N1) 2009 cases.

In summary, the methodology attempts to adjust for the proportion of patients contacting the NPFS, but has continued to use Primary Care attendance (QSurveillance) and positivity rates from 'swabbing' practices within sentinel GP schemes (RCGP and RMN). These have been estimated from a 'mixed effects logistic regression model' using data by age group and Strategic Health Authority (some SHAs are grouped). The effects of NPFS on these other surveillance sources are uncertain and although adjusted for in the analysis, may be greater (or less) than that allowed. The introduction of these changes at the same time as school closures, which may well impact on transmission, mean that there are still uncertainties in the estimated figure.