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Volume 3 No 43; 30 October 2009

Cryptosporidiosis associated with swimming pools

Outbreaks of cryptosporidiosis have been frequently associated with swimming pools in recent years and these tend to be more common in the second half of the year [1]. This appears to have been the pattern of incidence in England and Wales this year to date, with a number of clusters or outbreaks having been reported associated with pools in recent weeks. Besides swimming pool use, circumstantial evidence suggests that foreign travel - implicated in two of the clusters/outbreaks, listed below - may also be a risk factor associated with increased incidence in the second half of the year.

Recently reported clusters/outbreaks include the following:
  • a large outbreak at a leisure centre in Merthyr Tydfil involving more than 100 cases [2];
  • seven cases in Greater Manchester associated with a swimming pool used predominantly by mothers and babies;
  • five cases linked to a swimming pool at a caravan park in Yorkshire;
  • four cases linked to a holiday park in the East Midlands that was visited during August Bank Holiday;
  • a cluster of five cases among individuals who had swum at the same pool in the Thames Valley area (and other travel-related cases is the same area) that are currently under investigation; and
  • 32 cases in West Yorkshire, where the source of infection remains unclear, of which 21 had recently been in a swimming or paddling pool and 15 had recently returned from abroad.

In addition to the above, other clusters of cases have been reported that have yet to be attributed to a source. As many of the clusters involve low numbers of cases, providing clear evidence of an association with a swimming pool can be difficult. Outbreaks related to pools can occur across a number of pools within an area [3].

Incidence of cryptosporidium infections in the first half of the year (mostly Cryptosporidium parvum) has declined since 2000 while incidence in the second half has remained broadly similar (predominantly Cryptosporidium hominis ) [4]. However, the cumulative total of cases in England and Wales in 2009, to week 40, exceeded the number for the same period of 2008 by 500 (figure 1).

Figure 1. Cumulative number of cases of Cryptosporidium spp infection per week in England and Wales 2004 to 2009

The significant decrease in cryptosporidiosis cases in the first half of the year between the periods pre- and post-2001 (figure 2) is thought to reflect improvements in drinking water treatment [5,6] and this emphasises that effective targeted intervention can result in dramatic reductions in disease. Nevertheless, intervening to prevent outbreaks linked to pools can be difficult [3], particularly where the pool is located in a holiday resort in another country. In 2003, for example, a large, late-summer outbreak of cryptosporidiosis occurred as a result of contaminated swimming pools in Majorca [7].

Figure 2. Average number of cases of Cryptosporidium spp infection per week in England and Wales 1990 to 2008

There is no regulation of the microbiological quality of swimming pools and monitoring pool standards has relied on microbiological indicators (E. coli, coliforms, Pseudomonas aeruginosa and aerobic plate count) that have no value as predictors of cryptosporidium contamination. Within England and Wales, most testing for cryptosporidium has been associated with outbreaks. A study in the US found 8% of 160 randomly chosen pools were positive for Giardia or cryptosporidium or both with 1.8 % containing cryptosporidium, or cryptosporidium and giardia and 6.2% with giardia only [8]. Posters can be used to advise parents not to take their children swimming when they have diarrhoea or for two weeks after but this is an area that relies on parental responsibility and is difficult to monitor the effectiveness of such advice. Showering pre-swim is thought to reduce contamination of pool water. Local Authorities are responsible for ensuring that pools operate in a safe manner.

Outbreaks associated with pools may occur less frequently if industry best practice, as outlined in recently published guidance produced by the Pool Water Treatment Advisory Group [9], is followed. The guidance is an expanded and updated version of that first published in 1999 and covers the design, treatment, management, monitoring and outbreak management of pools of all sorts.

References

1. Nichols G, Chalmers RM, Lake IR, Sopwith W, Regan M, Hunter P et al. Cryptosporidiosis: A report on the surveillance and epidemiology of Cryptosporidium infection in England and Wales. 1-142. 2005. Drinking Water Inspectorate.
2. Further update on the cryptosporidium outbreak in South East Wales, Health of Wales Information Service, 17 September 2009, http://www.wales.nhs.uk/newsitem.cfm?ContentID=13128.
3. Puech MC, McAnulty JM, Lesjak M, Shaw N, Heron L and Watson JM (2001). A statewide outbreak of cryptosporidiosis in New South Wales associated with swimming at public pools. Epidemiol. Infect. 126: 389-396.
4. Chalmers RM, Elwin K, Thomas AL, Guy EC and Mason B (2009). Long-term Cryptosporidium typing reveals the aetiology and species-specific epidemiology of human cryptosporidiosis in England and Wales, 2000 to 2003. Euro. Surveill 14(2).
5. Lake IR, Nichols G, Bentham G, Harrison FC, Hunter PR and Kovats SR (2007). Cryptosporidiosis decline after regulation, England and Wales, 1989-2005. Emerg. Infect. Dis. 13: 623-625.
6. Sopwith W, Osborn K, Chalmers R and Regan M (2005). The changing epidemiology of cryptosporidiosis in North West England. Epidemiol. Infect. 133: 785-793.
7. Galmes A, Nicolau A, Gomis E, Guma M, Hernandez-Pezzi G and Soler P (2003). Cryptosporidiosis outbreak in British tourists who stayed at a hotel in Majorca, Spain. Euro. Surveill 7(33).
8. Shields JM, Gleim ER and Beach MJ (2008). Prevalence of Cryptosporidium spp. and Giardia intestinalis in swimming pools, Atlanta, Georgia. Emerg. Infect. Dis. 14: 948-950.
9. Pool Water Treatment Advisory Group (2009) Swimming Pool Water: Treatment and Quality Standards. PWTAG Ltd (www.pwtag.org).

Seventh HPA annual report on infections in injecting drug users

The seventh HPA report on infections among injecting drugs users (IDUs), Shooting Up [1], summarises surveillance data for 2008 derived from a range of systems used to monitor bacterial and viral infections in the UK. These systems include the Unlinked Anonymous Prevalence Monitoring Programme (UAPMP) survey of IDUs in contact with specialist services in England, Wales and Northern Ireland.

The report focuses in particular on the infections to which IDUs are vulnerable and that can cause significant morbidity and mortality, ie viruses – such as HIV, hepatitis C (HCV) and hepatitis B (HBV) – and bacterial infections – such as Clostridium botulinum and group A streptococci.

The main findings from the UAPMP survey* are that:
  • transmission of HIV and HCV infection through injecting drug use remains higher than a decade ago, with around a fifth (22%, 87 of 391) of recent initiates (ie those who started injecting drugs during the three years prior to participating in the survey) having antibodies to hepatitis C and one in 77 (1.3% 5 of 391) having HIV in 2008 (see figure 1). Overall in 2008, 40% (1,274 of 3,209) injecting drug users were infected with hepatitis C and 1.6% (51 of 3,209) with HIV;
  • around one third (31%, 654 of 2,138) of IDUs reported having had an abscess, sore or open wound at an injecting site in the last year. These infections may place considerable burden on the NHS;
  • uptake of testing for HCV among IDUs in contact with drug services, after increasing markedly, now appears to be levelling off. In England only 23% of IDUs (643 of 2,757) reported never having had a voluntary confidential testing (VCT) for HCV in 2008 compared with 51% (1,532 of 2,998) in 2000. Of participants from Wales 35% (159 of 456) reported never having a VCT for hepatitis C in 2007/08, whilst less than one in ten (7.6%, 23 of 302) of the participants from Northern Ireland in 2007/08 reported not having had a VCT for hepatitis C;
  • most IDUs in contact with services report having had a VCT for HIV at some point with 28% of IDUs (863 of 3,087) reporting never having had such test in 2008;
  • the transmission of hepatitis B continues among IDUs. However, this may have declined in recent years. Around one in six IDUs (13%, 425 of 3,207) had been infected with hepatitis B in 2008. There has been a marked increase in the number of IDUs receiving the hepatitis B vaccine, with almost three-quarters (72%, 2,259 of 3,140) now reporting uptake of the vaccine; and
  • levels of reported needle and syringe sharing have declined in recent years following an increase in the late 1990s. In 2008, almost a fifth (19%, 343 of 1,798) of current injectors reported sharing injecting equipment in the previous month (see figure 2).

* UAPMP survey collects Oral Fluid samples. The sensitivity of the Oral Fluid test used for HCV is approximately 92%, and that for hepatitis B core antigen around 75%.

Figure 1. The prevalence of HIV infection among recently* initiated injecting drug users England, Wales & Northern Ireland^: 1998 to 2008

* Those who started injecting drugs during the three years prior to participating in the survey.
^ Includes Northern Ireland from 2002.
Data from Unlinked Anonymous Prevalence Monitoring Programme survey of injectors in contact with drug agencies.

Figure 2. The sharing of needles and syringes & any injecting equipment* among current injectors** in England, Wales & Northern Ireland^: 1998 to 2008


* Needles, syringes, filters, mixing containers, or water.
** Those who injected drugs during the four weeks prior to participating in the survey.
^ Includes Northern Ireland from 2002.
Data Source: Unlinked Anonymous Prevalence Monitoring Programme survey of injectors in contact with drug agencies.

The report's findings indicate a continuing need to develop services to reduce injection-related harms and to support those who want to stop injecting, in line with published guidelines [2,3,4,5,6,7]. They also underline the continuing importance of public health surveillance of diseases and behaviours associated with the injection of drugs as a means developing policies and services to reduce infections among IDUs.

References

1. Health Protection Agency, Health Protection Scotland, National Public Health Service for Wales, CDSC Northern Ireland, and the CRDHB. Shooting Up: infections among injecting drug users in the United Kingdom 2008. London: Health Protection Agency, October 2009.
2. Hope V et al. “Frequency, factors and costs associated with injection site infections: findings from a national multi-site survey of injecting drug users in England”, BMC Infectious Diseases 2008, 8:120.
3. Drug misuse and dependence – guidelines on clinical management: update 2007. London: Department of Health, 2007.
4. Drug misuse: psychosocial interventions. NICE, Clinical Guideline, CG51, July 2007. Available at: http://guidance.nice.org.uk/CG51.
5. Drug misuse: opioid detoxification. NICE, Clinical Guideline, CG52, July 2007. Available at: http://guidance.nice.org.uk/CG52.
6. Models of care for the treatment of adult drug misusers. National Treatment Agency for Substance Misuse. London, 2006. MOC3.
7. Needle and syringe programmes: providing people who inject drugs with injecting equipment. NICE, Public Health Guidance, PH18, February 2009. Available at: http://guidance.nice.org.uk/PH18.

Fifth annual report on infections in blood and tissue donors and transfusion recipients in the UK

The NHS Blood and Transplant (NHSBT)/Health Protection Agency (HPA) Centre for Infections Epidemiology Unit runs a series of national schemes which provide epidemiological information about bloodborne infections in blood, tissue and cell donors in the UK and the associated risk of transmission via transfusion or transplantation, in order to inform donor practices and public health.

The NHSBT/CfI Epidemiology Unit's fifth annual report [1] presents national data for 2008 from all the schemes within the NHSBT/HPA programme, and aims to describe the data collected and any trends observed. The report also details some of the applications of the data including the estimated risks of current donation testing strategies not identifying an infectious donation. Information about antenatal samples tested by NHSBT is also presented.

Key information in the 2008 report includes:
  • Syphilis was the most frequently detected infection in blood donations in 2008. An increasing proportion of new blood donors probably have recently-acquired syphilis infections.
  • The frequency of HIV infection has been slowly increasing since 1996, while HIV seroconversions have also increased in recent years. In 2008, almost half of HIV-infected donors should not have donated according to current donor selection guidelines, if their risk exposure had been declared when they donated.
  • The proportion of antenatal samples tested by NHSBT that was positive for HBsAg increased again in 2008 to 0.35%. Susceptibility to rubella also increased to 3.2% of all samples tested.
  • The overall frequency of infection in tissue and cord blood donors tested by NHSBT was lower in 2008 (121.9 infections per 100,000 donors tested) as compared to 2007 (273 infections per 100,000 donors tested), although this is still higher as compared to first-time blood donors.
  • There were four confirmed reports of bacterial transfusion transmitted infection (TTI) in 2008, involving the transmission of infection to a total of six recipients. There have been no confirmed reports of viral TTI for the third consecutive year.
  • Up to date estimates for the residual risk of a viral infection entering the blood and tissue supply, despite donor testing, are included and show that the probability of acquiring hepatitis B, hepatitis C, HIV or HTLV via blood transfusion was very low between 2006 and 2008.

Additional data (available in slide set and pdf format) [2] and information about the unit's data sources and collection methods [3] are available from the Bloodborne Infections in Blood Donors (BIBD) pages of the HPA website and surveillance data are published periodically in the Health Protection Report.

Data from the transfusion-transmitted infection surveillance scheme form part of the haemovigilance collaboration known as SHOT ("serious hazards of transfusion", http://www.shotuk.org) which aims to build an evidence base on transfusion hazards.

References

1. Safe supplies: testing the nation. Annual report from the NHS Blood and Transplant/HPA Centre for Infections Epidemiology Unit, 2008. Available from the HPA website at Topics >Infectious Diseases >Reference Library >BIBD References and Publications, http://www.hpa.org.uk/infections/topics_az/BIBD.

2. Supplementary data tables, Annual report from the NHS Blood and Transplant/HPA Centre for Infections Epidemiology Unit, 2008. HPA website: BIBD References and Publications.

3. NHS Blood and Transplant/Health Protection Agency Epidemiology Unit: data sources and methods (August 2009). HPA website: BIBD References and Publications.

Pandemic influenza: UK situation at 29 October 2009

The Health Protection Agency's Weekly National Influenza Report of 29 October (week 44) [1] described the UK (and international) situation as follows:
  • Pandemic influenza activity increased across the UK, the main burden of disease remaining in school-aged children and young adults;
  • In week 43 (week-ending 25 October), the weekly influenza/ILI consultation rates increased, and were above the winter baseline thresholds in England, Scotland and Northern Ireland;
  • The National Pandemic Flu Service (NPFS) continued to issue antiviral drugs to people in England with an influenza-like illness who called or logged on to the internet site. The number of assessments and anti-viral collections has continued to increase gradually over the past week;
  • Forty-two schools throughout England, and 12 in Northern Ireland, reported outbreaks of ILI in week 43;
  • Interpretation of data to produce estimates on the number of new cases continued to be subject to a considerable amount of uncertainty with the move to NPFS. HPA modelling gave an estimate of 78,000 (range 39,000 - 169,000) new cases in England in week 43. The estimated number of new cases increased in all regions and age groups;
  • The main influenza virus circulating in the UK continued to be the pandemic (H1N1) 2009 strain, with few influenza H1 (non-pandemic), H3 and B viruses detected. Three of 2050 pandemic viruses tested have been confirmed to carry a mutation which confers resistance to the antiviral drugs oseltamivir; all three are phenotypically resistant to the drug but retain sensitivity to zanamivir;
  • The majority of pandemic influenza cases continued to be mild. The cumulative number of deaths reported due to pandemic (H1N1) 2009 in the UK was 135. There was a total of 1200 new patients hospitalised with suspected pandemic influenza in the week 22 to 28 October, an increase from 884 in the previous week. The highest hospitalisation rates have consistently been in the under-5-year age group and have increased in all age groups recently;
  • According to the European Centre for Disease Prevention and Control (ECDC), by 28 October, 5938 deaths due to pandemic influenza had been reported globally;
  • According to the World Health Organisation (23 October), influenza activity is low in temperate southern hemisphere regions, is increasing in the temperate northern hemisphere regions and has declined in most tropical areas.

References
1. HPA. Weekly National Influenza Report: week 44 (29 October 2009, PDF 400 KB), HPA website: www.hpa.org.uk/swineflu/surveillance&epidemiology.