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Salmonella

 

General Information

Salmonella is a rod-shaped bacterium that can cause diarrhoeal illness in humans. The vast majority of these belong to the species Salmonella enterica. This has more than 2000 different types (called serotypes or serovars) which are found in a variety of environments.  The bacterium can be found in the gastrointestinal tract of wild and domestic animals, birds (especially poultry), reptiles, amphibians (for example, terrapins), and occasionally humans.  
  
Of the many Salmonella enterica serotypes that can cause human illness, Salmonella Enteritidis and Salmonella Typhimurium are the most common in the United Kingdom and account for over half of all laboratory-confirmed human infections in Wales.
 
One subspecies called Salmonella Typhi (not to be confused with Salmonella Typhimurium) and which is only found in humans can lead to a severe  systemic (generalised) illness, commonly known as typhoid fever or enteric fever. This disease is transmitted from human to human via humans contaminating food or drinking water. It is therefore mainly hygiene and sanitary conditions that determine its spread. It is primarily for this reason that it is no longer so commonly seen in industralised countries although it is still endemic in developing countries. Vaccination against typhoid fever for UK travellers to endemic regions is recommended.
 
More usually, infection with salmonella causes watery and ocassionally bloody diarrhoea, abdominal pain, headache, nausea, vomiting, and fever. The illness can range from mild to severe. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness. In some cases, the salmonella infection may spread from the intestines to the blood stream, and then to other body sites.
 
The majority of patients with infections caused by salmonella do not require specific treatment and make a full recovery although a few patients later experience reactive arthritis, which can have long-lasting, disabling effects. If infection spreads from the intestines to the blood stream, prompt hospital treatment with certain antibiotics is required.
 
Since the beginning of the 1990s, strains of salmonella which are resistant to a range of antimicrobials, including first-choice agents for the treatment of humans, have emerged and are threatening to become a serious public health problem. This resistance results in part from the use of antimicrobials both in humans and animal husbandry. More about the emergence of antimicrobial resistant salmonella strains is given on the World Health Organisation website at: http://www.who.int/mediacentre/factsheets/fs139/en/
 
Salmonella infection in the UK is frequently associated with eating foodstuffs (most commonly meat, raw eggs, unpasteurised milk and dairy products) containing the bacterium. This usually follows contamination of cooked food by raw food or by failing to achieve cooking temperatures that are adequate to kill the bacteria. Cases can be prevented by the correct storage and cooking of foods and employing hygienic food handling and preparation procedures. Avoidance of certain foods, for example milk and dairy products that are unpasteurised and raw eggs can also lower the risk of illness. Salmonella infection can also be caught by handling animals and reptiles such as iguanas, turtles and terrapins.
 
Advice on the safe preparation, storage, cooking and handling of food is available from the Food Standards Agency website. Washing hands thoroughly before eating or preparing food, after using the toilet, changing nappies or cleaning up after others with diarrhoea and after contact with domestic or farm animals can also prevent infection.
 
General information about salmonella infection is available on the main Public Health Wales website at: http://www.wales.nhs.uk/sitesplus/888/page/43751
 
Further information about salmonella is available from the following websites:
Further information about typhoid fever (S. Typhi) is available from the following websites:

 

Epidemiology

Salmonella Typhi and Salmonella Paratyphi

In the UK before the middle of the twentieth century, the main human illnesses associated with salmonella infection were typhoid fever and, the usually milder, paratyphoid fevers (collectively known as enteric fever), caused by the subtypes S. Typhi and S. Paratyphi respectively. These two subspecies are only adapted to live in humans and are transmitted by the fecal-oral route i.e. excreted by humans in faeces and transmitted by contaminated water, food, or by person-to-person contact. Improvemnets in sanitation during the last century led to the dramatic decline in cases of both typhoid and paratyphoid fevers in the UK.
  
However, both typhoid and paratyphoid fever are still highly prevalent in some regions of the world where sanitation is poor. The World Health Organization (WHO) estimates that 16 to 33 million cases of typhoid fever occur each year, with 500,000 to 600,000 deaths (a case fatality rate of between 1.5 and 3.8%). There are no WHO estimates of the annual incidence of paratyphoid; however, a study in 2004 estimated that 5.4 million cases of paratyphoid occur each year.
 

The majority of typhoid occurs in Asia, Africa, and Latin America where frequent outbreaks are reported. Outbreaks have also been reported in eastern Europe and central Asia, and since 2004, small scale outbreaks have occurred in Kyrgyzstan, the Ukraine and Russia.

In the UK, typhoid fever and paratyphoid fever usually occur in travellers who have visited or are arriving from endemic areas. Occasionally cases occur following transmission from a returned traveller (usually within family or household settings), or rarely, from chronic carriers.
 
During 2012 Public Health England (PHE) reported 354 cases of enteric fever in England and Wales, five of which were in Wales. Of these, 329 (93%) were presumed to have acquired the infection abroad. These data are available from the PHE website at http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1317140635485
 
More about the epidemiology of typhoid and paratyphoid is available from:
 
Salmonella Typhimurium and Salmonella Enteritidis
 
Infection with salmonella does not appear to have been a common occurrance in England and Wales before 1940. Data from the Ministry of Health and the Public Health Laboratory Service (PHLS) show that between 1936 and 1940, only 38 incidents of illness due to salmonella infection were recorded (an incident is defined as either a single, sporadic case or an outbreak of two or more related cases).
 
Published PHLS annual reports on food poisoning show an increase of incidents of salmonella from 65 in 1941 to 9461 in 1982. Although, part of this increase is undoubtably due to better reporting of illness and increased laboratory testing facilities, this rise in cases accompanied changes in the patterns of food production (i.e. more intensive farming practices), processing, distribution and consumption.
 
Until the late 1980s, S. Typhimurium was the predominant serotype causing illness in humans with S. Enteritidis accounting for very low levels of infection. However, cases of salmonella due to S. Enteritidis (most particularly S. Enteritidis phage type 4) increased markedly from 1986, reaching a peak of infection in 1997. This rise was associated with infection of the worldwide egg-laying hen flock with this strain of salmonella and the ability of S. Enteriditis PT4 to be passed into the inside of the eggs laid by infected chickens.
 
Rates of infection due to S. Enteritidis in Wales and the UK have since fallen dramatically. This falling trend may be attributable to many reasons including greater public awareness about food safety but the most important factor is the compulsory vaccination of the UK egg-laying flock, introduced in 1998, against Salmonella Enteritidis
 
Salmonella infections peak in the summer months (see next section). This may result from the warm weather enabling the bacteria to multiply in conditions where food hygiene practices are poor and different eating habits in the summer months, with more cold food consumed, more buffets where food is left for long periods before consumption and more barbecues.
 
Other salmonella serovars
 
Outbreaks due to different salmonella serovars also occur sporadically. A UK-wide outbreak of Salmonella Montevideo ocurred between February and June 2006 and was linked to the consumption of salmonella-contaminated chocolate confectionary manufactured by one supplier and distributed nationwide. In late 2007-early 2008 a UK-wide outbreak of Salmonella Anatum was identified with custard-based products suspected as being the source of the outbreak based on descriptive evidence. Between February and August 2008, an outbreak of Salmonella Agona affecting 10 European countries occured with 163 reported cases, 11 of which were from Wales. A link was established between the outbreak and a factory in the Republic of Ireland manufacturing cooked meat products.
 

Rates of salmonella infection in Wales

Reports of the rates and numbers of laboratory-confirmed salmonella infections (all Salmonella, Salmonella Enteritidis, Salmonella Typhimurium, Salmonella Typhi and Salmonella Paratypi types A and B) in Wales are published monthly and are available to download from: Monthly All-Wales Laboratory-Confirmed Infections and Notifications Reports

Time trend data using CoSurv laboratory/notification data for laboratory-confirmed salmonella infection and for food poisoning notifications for Wales from 1993 can be generated interactively from this website on an individual Local Authority basis. 
  
The yearly geographical distribution of salmonella infection in Wales from 1997 is also available. Please use the link below to access the interactive trend data tool on this website:
Please note: these data may vary from PHE reports
 
Laboratory reports of Salmonella sp, Salmonella Enteritidis and Salmonella Typhimurium in Wales: 1980-2013
   
        Salmonella spp, S. Enteriditis and S. Typhimurium 1981-2013 
Source: Public Health England Centre for Infections: LabBase, 1980-1992 and CDSC Wales: Monthly Laboratory confirmed infections report http://www.wales.nhs.uk/sites3/page.cfm?orgid=457&pid=27920 
Data retrieved 26/03/14. Please note that data, particularly for the most recent years, may change due to late reporting.
 
Laboratory reports of Salmonella sp, Salmonella Enteritidis and Salmonella Typhimurium in Wales: 1981-2014*
   

Year

Number of laboratory confirmed cases

Rate of all Salmonella per 100,000 population

All Salmonella

Salmonella Enteritidis

Salmonella Typhimurium

1981

489

30

216

17.4

1982

624

31

312

22.3

1983

533

76

208

19.0

1984

596

72

285

21.3

1985

457

101

163

16.3

1986

737

217

283

26.2

1987

759

332

239

26.9

1988

896

552

226

31.5

1989

1176

626

346

41.2

1990

1322

811

253

46.2

1991

1416

845

386

49.3

1992

1957

1304

357

68.0

1993

1866

1055

256

64.8

1994

1747

892

328

60.6

1995

1891

758

513

65.5

1996

1566

807

265

54.2

1997

2320

1307

288

80.3

1998

1556

865

162

53.8

1999

902

379

98

31.2

2000

685

299

112

23.6

2001

717

322

88

24.6

2002

600

252

46

20.5

2003

725

308

62

24.7

2004

694

250

56

23.5

2005

613

190

49

20.6

2006

546

169

49

18.3

2007

543

170

26

18.1

2008

599

135

47

19.8

2009

454

142

48

14.9

2010

469

102

90

15.4

2011

456

103

83

14.9

2012

409

72

64

13.3

2013

407

82

69

13.2

2014*

51

7

6

1.7

Source: Public Health England Centre for Infections: LabBase, 1980-1992 and CDSC Wales: Monthly Laboratory confirmed infections report http://www.wales.nhs.uk/sites3/page.cfm?orgid=457&pid=27920
*Data for 2014 at 26/03/14. Please note that data, particularly for the most recent years, may change due to late reporting. 
 
Laboratory reports  of all Salmonella in Wales by month: 2008 - 2014
 
        Salmonella: cases by month per year 2008-2014
 
Source: CDSC Wales: Monthly Laboratory confirmed infections report: http://www.wales.nhs.uk/sites3/page.cfm?orgid=457&pid=27920 
Data retrieved 26/03/14. Please note that data, particularly for the most recent years, may change due to late reporting.  
 
Laboratory reports of Salmonella Typhi and Salmonella Paratyphi types A and B: 1980-2013
  
        Salmonella: Typhi and Paratyphi by year 1980-2013
Source: CDSC Wales: Monthly Laboratory confirmed infections report: http://www.wales.nhs.uk/sites3/page.cfm?orgid=457&pid=27920 
Please note that data, Please note that data, particularly for the most recent years, may change due to late reporting. 
 
Laboratory reports of Salmonella Typhi and Salmonella Paratyphi types A and B: 1980-2014*
  

Year

Number of laboratory confirmed cases

Salmonella Typhi

Salmonella Paratyphi types A and B

1980

4

11

1981

6

4

1982

2

3

1983

11

5

1984

10

2

1985

6

7

1986

10

1

1987

6

7

1988

2

2

1989

4

1

1990

1

3

1991

3

1

1992

3

4

1993

3

2

1994

2

3

1995

5

8

1996

1

3

1997

4

3

1998

3

1

1999

1

3

2000

1

1

2001

8

1

2002

2

0

2003

1

3

2004

3

4

2005

0

4

2006

1

4

2007

3

6

2008

12

0

2009

3

2

2010

16

2

2011

8

0

2012

4

1

2013

6

5

2014*

0

0

Source: CDSC Wales: Monthly Laboratory confirmed infections report: http://www.wales.nhs.uk/sites3/page.cfm?orgid=457&pid=27920
Data for 2014 at 26/03/14. Please note that data, particularly for the most recent years, may change due to late reporting.  
 
 

Sources of surveillance data for Wales

In Wales, salmonella  infection is confirmed by laboratory testing of faecal or more rarely, blood or other samples. Further typing may be undertaken to establish what serovar of salmonella is present.
 
Laboratory confirmed data for salmonella in Wales is compiled by our databases and it is these data that is used to generate data from 1992 onwards. Before this date, the HPA LabBase dataset has been used.
 
Notification data: Salmonella is one of a number of organisms which give rise to gastro-intestinal illness. Gastro-intestinal infections that are foodborne are categorised as food poisoning. Food poisoning is a notifiable infectious disease in Wales and the UK. Numbers of food poisoning notifications for Wales are collated on a weekly basis by Public Health Wales: view surveillance data for food poisoning in Wales
 
Salmonella is identified as the causative agent in a proportion of food poisoning notifications after laboratory testing. Additional testing may also be undertaken to determine the serovar of Salmonella present.
 
Enhanced surveillance of enteric fever: Reported cases of enteric fever in England and Wales have been increasing in recent years. To better understand the epidemiology of both travel-associated and non-travel-associated enteric fever and to assess its impact on the UK more accurately, an active national surveillance scheme for enteric fever in England, Wales and Northern Ireland was introduced on 1 May 2006 managed by Public Health England. As of 1 Feb 2012, health protection practitioners and environmental health officers are requested to use the national questionnaire below for reporting all cases of enteric fever to the national surveillance system. 
 
 

The Welsh Food Microbiological Forum (WFMF)

The WFMF co-ordinates consistent sampling and collates data and information on the quality of ready-to-eat food in Wales including levels of salmonella  in raw retail chicken. More information about the Welsh Food Microbiological Forum and reports on their findings are available from the Health Protection Internet site which can be accessed from the following link: Welsh Food Forum
  

Requests for further surveillance data

If further surveillance data for salmonella in Wales is required, it may be possible to provide it on special request. Please use the surveillance data request form provided from this link.
  

Links to other salmonella surveillance

 


Last updated: 28/03/2014