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Final Issue: Volume 16 Number 51
Published on: 21 December 2006
Final Issue in PDF
Last updated: Volume 15, No.11 (PDF file, 815 KB)
North East London Health Protection Unit has been investigating and managing an outbreak of Salmonella Enteritidis phage type 1 (PT1) linked to a kebab shop in north east London. The outbreak appears to be associated with rapid onset of what was often severe illness, and with an unusually high attack rate.
The Unit was first alerted to the incident on Saturday 12 February 2005 following presentation of 31 patients with food poisoning symptoms to a London hospital accident and emergency (A&E) department. With increasing numbers of patients presenting to A&E, the hospital had to close to new admissions. The kebab shop was closed voluntarily at 1:00 pm, Saturday 12 February, following a visit by Environmental Health Officers.
One hundred and ninety-five cases have now been reported from various sources, 87 of whom have been confirmed by the Health Protection Agency’s Laboratory of Enteric Pathogens as infected with S. Enteritidis PT1, with resistance to nalidixic acid and reduced susceptibility to ciprofloxacin (NxCpL) Another 12 specimens are positive for salmonella spp and awaiting typing. All patients reported having eaten food at the same kebab shop in north east London. Most patients were seriously ill with diarrhoea, vomiting, and fever. Some suffered from dehydration and confusion. A number of patients were admitted with possible systemic infection. Food and environmental samples were taken. The proprietors were interviewed and it was reported that three staff members had been unwell since early on 11 February. Clinical specimens were taken from all six staff, three of whom tested positive for the same salmonella strain. Assessment of the kebab shop after the outbreak identified a number of potential risk areas that could have caused cross-contamination.
London Food Water and Environment microbiology laboratory (LFWE) tested 38 food samples from the shop and two samples from patients’ homes, of which 14 were positive for S. Enteritidis PT1 (NxCpL). S. Enteritidis PT1 is the second most common salmonella strain in the United Kingdom (UK) and has been recently associated with Spanish eggs and poultry, or travel to Spain (1). A sample of 120 eggs was later obtained from the shop’s supplier but tested negative. Twenty environmental samples were also taken from the shop, one of which (a duster/wiping cloth) was positive for S. Enteritidis PT1 (NxCpL).
Eight food samples were positive for Clostridium perfringens toxin six of which were also positive for S. Enteritidis PT1. C. perfringens toxin was detected in one of 12 stool samples; this was a co-infection with S. Enteritidis PT1 (NxCpL).
Analysis of 76 outbreak questionnaires by the Health Protection Unit indicated that 70% of interviewed patients were male and 80% were aged under 40 years. Almost all of the patients (94%) reported having eaten at the kebab shop on Thursday, 10 February, and presented with symptoms (87%) on Friday, 11 February (figure). The incubation period was less than 12 hours for two-thirds of the patients. Approximately one quarter of the interviewed patients spent one night or more at the hospital. Symptoms included diarrhoea, vomiting, abdominal pain, fever, nausea, and headaches. Food items such as chilli sauce, mayonnaise, salad, and chicken doner were each reported as eaten by more than 60% of patients.
Figure Epidemic curve of Salmonella Enteritidis PT1 outbreak in north east London , interviewed cases only*
|*In total 75 cases shown, but onset time not available for one additional case not shown on figure.|
Only two other people were identified as possibly having eaten food from the restaurant and not having developed symptoms. Based on this observation, the attack rate appears to be very high but, in the absence of a comprehensive list of those who had food at the restaurant on Thursday and Friday, it is not possible to determine the rate precisely. Based on an estimated 300 to 400 portions of food served each day and a reported 195 symptomatic cases the attack rate currently appears to be around 50%.
Around 2000 cases of S. Enteritidis PT1 are reported each year in the UK, some as part of outbreaks. The north east London outbreak is the largest UK outbreak reported to date.
1.Health Protection Agency. Salmonella Enteritidis outbreak in central London linked to Spanish eggs. Commun Dis Rep Wkly [serial online] 15 January 2005 [cited 16 March 2005]; 14(3): News. Available at: <.http://www.hpa.org.uk/cdr/archives/2004/cdr0304.pdf>.
To date, one hundred isolates of community methicillin resistant Staphylococcus aureus (C-MRSA) have been confirmed microbiologically in England and Wales over the last three years. An additional 40 isolates of suspected C-MRSA are currently undergoing characterisation. This represents less than 0.005% of the MRSA isolates received by the Health Protection Agency’s Staphylococcus Reference Laboratory (SRL) each year. Healthcare personnel need, however, to be aware of possible changes in the epidemiology of MRSA nationally and remain vigilant, particularly as C-MRSA is resistant to agents most likely to be prescribed for S. aureus infection in the community (ie, β-lactams).
In contrast to healthcare-associated MRSA (HCA-MRSA), C-MRSA has been identified in previously healthy individuals without recognised risk factors such as previous hospitalisation, recent antimicrobial therapy, indwelling catheters, prior invasive or surgical procedures. C-MRSA typically causes skin and soft tissue infections such as furuncles, cellulitis, and skin abscesses, occasionally requiring surgical incision and drainage. It has, however, been associated with a range of clinical manifestations from asymptomatic carriage through to life-threatening invasive infections such as bacteraemia, endocarditis, osteomyelitis, necrotising pneumonia with occasional fatal infections in previously healthy paediatric patients and young adults (1,2).
The term C-MRSA is ill-defined and isolates have variously been referred to as community-acquired, community onset, or community MRSA. Arbitrarily defining MRSA infections that are apparent in the first 48 to 72 hours of admission to hospital as ‘community-acquired MRSA’ has led to confusion and should be avoided. For example, prior healthcare exposure can lead to the mis-identification of ‘overspill’ healthcare-associated MRSA (HCA-MRSA) into the community as C-MRSA. There is genetic evidence that ‘genuine’ C-MRSA strains are distinct from HCA-MRSA, so reliance on definitions based on whether infection was present prior to admission may overestimate the prevalence of true C-MRSA. As C-MRSA exhibits considerable genetic heterogeneity, and multiple independent clonal lineages occur worldwide, the characterisation of MRSA using genotypic techniques is necessary to identify isolates of community origin as C-MRSA and differentiate them reliably from healthcare-associated isolates.
C-MRSA differs from HCA-MRSA in a number of ways. For example, the hallmark features of C-MRSA include:
There is a lack of data on the prevalence of C-MRSA strains in England and Wales. Extensive characterisation of isolates referred to the SRL has shown that C-MRSA has been occurring nationally since at least 2001 (5,6). To date, four distinct clonal lineages of C-MRSA have been identified among isolates submitted to the Reference Laboratory, three of which encode the PVL gene (table).
Table Characteristics of C-MRSA clones in England and Wales
|Sequence type (MLST*)||ST1||ST8||ST30||ST80|
|Panton Valentine Leukocidin (PVL) gene||Negative||Positive||Positive||Positive|
Infection caused by organisms from a PVL-negative clonal lineage (ST1) have been associated mainly with injecting drug users throughout England and Wales (5), causing injection site abscesses and bacteraemia. This clone exhibits a distinctive antibiogram, susceptible to ciprofloxacin, but resistant to fusidic acid and, occasionally, erythromycin. A PVL-positive clone (ST8), reported to be widespread in the United States has been identified in a small number of patients in three geographically distinct centres. These isolates are resistant to ciprofloxacin and, occasionally, erythromycin. A second PVL-positive clone (ST30), reported to occur widely in the southern Pacific, is resistant to tetracycline and erythromycin. A third PVL-positive C-MRSA (ST80) has been identified in various locations throughout England and Wales and has been observed elsewhere in Europe (7). This lineage is susceptible to ciprofloxacin, but commonly resistant to fusidic acid and tetracycline.
Organisms from these lineages have caused sporadic disease in the community among individuals attending their general practitioner, and out-patient and accident and emergency departments throughout England and Wales (5,6), with small clusters occurring in five cities in England. Patients of various age groups have generally presented with skin infections (boils, abscesses or cellulitis), bacteraemia or joint infections. One death in England, a woman aged 28 years presenting with community-acquired pneumonia, is known to have been associated with PVL-positive C-MRSA, as previously reported in the press.
Although these data suggest that low numbers of C-MRSA are occurring in the UK, it is important that their prevalence is monitored carefully in view of their emergence worldwide (7). To achieve this and improve case ascertainment, a useful marker for recognising putative C-MRSA in the clinical diagnostic laboratory is through analysis of antibiogram data (table) together with clinical and epidemiological data. Typically, C-MRSA is heterogeneously resistant to oxacillin and unusually susceptible to antimicrobials other than β-lactams, particularly ciprofloxacin. Isolates meeting these criteria, particularly from individuals with skin and soft tissue infection originating in the community, should be sent to the Staphylococcus Reference Laboratory, Centre for Infections, HPA, 61 Colindale Avenue, London NW9 5HT, for additional characterisation
For further information, please contact Angela Kearns at the Staphylococcus Reference Laboratory: tel 020 8327 7227; email : <email@example.com>.
1.Centers for Disease Control and Prevention. Four paediatric deaths from community-acquired methicillin-resistant Staphylococcus aureus – Minnesota and North Dakota, 1997-1999. MMWR Morbid Mortal Wkly Rep [serial online] 1999 [cited 10 March 2005]; 48: 707-10..
2.Gillet Y, Issartel B, Vanhems P, Fournet JC, Lina G, Bes M, et al. Association between Staphylococcus aureus strains carrying gene.
3.Huletsky A, Giroux R, Rossbach V, Gagnon M, Vaillancourt M, Bernier M, et al. New real-time PCR assay for rapid detection of methicillin- resistant Staphylococcus aureus directly from specimens containing a mixture of staphylococci. J Clin Microbiol 2004; 42:1875-84.
4.Enright MC, Day NP, Davies CE, Peacock SJ, Spratt BG. Multilocus sequence typing for characterization of methicillin-resistant and methicillin-susceptible clones of Staphylococcus aureus. J Clin Microbiol 2000 38:1008-15.
5.Kearns AM, Rathmann IR, Holmes A, Pitt TL, Cookson BD. An unusual clone of MRSA causing infection in injecting drug users. J Infect 2004; 49: 49-50.
6.Holmes A, Ganner M, McGuane S, Pitt TL, Cookson BD, Kearns AM. Staphylococcus aureus carrying Panton-Valentine leukocidin genes (PVL) in England and Wales: frequency, characterisation and association with clinical disease. J Clin Microbiol (in press).
7.Vandenesch F, Naimi T, Enright M C, Lina G, Nimmo G R, Heffernan H, et al. Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: worldwide emergence. Emerg Infect Dis 2003; 9: 978-84.
Three data values in this article, originally published on 23 December 2004, Vol 14 number 52, have been amended:
1. In the second sentence of the first paragraph , 'The main findings are: 6681' was changed to 'The main findings are: 6861'
2. In the first sentence of the second paragraph, 'London accounted for 45% of all cases reported' was changed to 'London accounted for 44% of all cases reported'
3. In the first sentence of paragraph five, 'cases with a known drug susceptibility result increased from 6.7 % in 2001 to 7.0% in 2002' has been amended to 'cases with a known drug susceptibility result increased from 6.7 % in 2001 to 7.1% in 2002'.