Trends in sexually transmitted infections (other than HIV) in older people: analysis of data from an enhanced surveillance system

OBJECTIVE

This study examines the distribution of selected sexually transmitted infections (STIs) in older people (aged >/=45 years) attending genitourinary medicine (GUM) clinics in the West Midlands, UK.

METHODS

Analysis of data from the regional enhanced STI surveillance system for the period 1996-2003. Selected STIs were chlamydia, genital herpes, genital warts, gonorrhoea and syphilis.

RESULTS

Altogether, 4445 STI episodes were reported among older people during the study period. Between 1996 and 2003 older people accounted for 3.7% and 4.3%, respectively, of all GUM clinic attendances. The rate of STIs in older people more than doubled in 2003 compared with 1996 (p<0.0001). Rates for all five selected diagnoses were significantly higher in 2003 compared to 1996. A significantly increasing trend over time was seen overall (p<0.0001) and for each of the selected diagnoses. Overall, males and those aged 55-59 years of age were significantly more likely to be affected.

CONCLUSIONS

This study provides evidence of significant increases in attendance at GUM clinics by older people. Although it is recognised that young people should remain the focus of sexual health programmes, the results indicate that sexual risk-taking behaviour is not confined to young people but also occurs among older people. There is therefore a need to develop and implement evidence-based multifaceted sexual health programmes that while aiming to reduce STI transmission among all age groups should include interventions aimed specifically at older people and address societal and healthcare attitudes, myths and assumptions about sexual activity among older people.

Understanding the transmission dynamics of respiratory syncytial virus using multiple time series and nested models

The nature and role of re-infection and partial immunity are likely to be important determinants of the transmission dynamics of human respiratory syncytial virus (hRSV). We propose a single model structure that captures four possible host responses to infection and subsequent reinfection: partial susceptibility, altered infection duration, reduced infectiousness and temporary immunity (which might be partial). The magnitude of these responses is determined by four homotopy parameters, and by setting some of these parameters to extreme values we generate a set of eight nested, deterministic transmission models. In order to investigate hRSV transmission dynamics, we applied these models to incidence data from eight international locations. Seasonality is included as cyclic variation in transmission. Parameters associated with the natural history of the infection were assumed to be independent of geographic location, while others, such as those associated with seasonality, were assumed location specific. Models incorporating either of the two extreme assumptions for immunity (none or solid and lifelong) were unable to reproduce the observed dynamics. Model fits with either waning or partial immunity to disease or both were visually comparable. The best fitting structure was a lifelong partial immunity to both disease and infection. Observed patterns were reproduced by stochastic simulations using the parameter values estimated from the deterministic models.

Enhanced surveillance of HIV infection in the West Midlands

The West Midlands Regional HIV Surveillance Project was set up in 1991 in response to a need for enhanced surveillance of HIV at a local level for service planning. The system showed that accurate and timely data could be collected whilst ensuring patient confidentiality. We present some of the data obtained from the system. HIV diagnoses continue to increase year on year, with certain population subgroups, including men who have sex with men and black Africans, disproportionately affected.

Surveillance of sexually transmitted infections in the West Midlands using anonymised individual patient datasets from genitourinary medicine clinics

Sexually transmitted infections (STIs) declined in the UK during the 1980s and early 1990s but have increased substantially since 1995. Within the overall increase there are important differences in the epidemiology of these infections. The current, aggregate system of STI data collection in the UK provides limited demographic information and is unable to fully explain these differences. More useful information can be obtained using an enhanced surveillance system that collects disaggregate, anonymised, individual patient data including ethnic group and truncated postcode of residence. Such a system has been set up in the West Midlands NHS region. The methodology of the project is described here along with the findings to date. These findings confirm that the burden of STIs disproportionately affects young persons, men who have sex with men, black ethnic minority groups and those living in urban areas. Identifying the groups at greatest risk in this way enables interventions to be more usefully targeted.

Long-term study of Cryptosporidium prevalence on a lowland farm in the United Kingdom

A longitudinal sample survey testing for Cryptosporidium in livestock and small wild mammals conducted over 6 years (1992-1997) on a lowland farm in Warwickshire, England, has shown the parasite to be endemic and persistently present in all mammalian categories. Faecal samples were taken throughout the year and oocysts concentrated by a formal ether sedimentation method for detection by immunofluorescence staining using a commercially available genus specific monoclonal antibody. Cryptosporidium parvum was identified by morphology and measurement of modified Ziehl-Neelsen stained oocysts. C. muris was rarely found in wild mammals and C. andersoni oocysts were never detected in livestock. Faecal samples from 3721 individuals gave cumulative 6-year prevalences for C. parvum as follows: bull beef, 3.6%; dairy cows, 3.5%; ewes, 6.4%; horses, 8.9%; calves (home bred), 52%; calves (bought-in) 23.2%; lambs, 12.9%; small wild mammals (rodents) living in and around farm buildings, 32.8%; small wild mammals (mainly rodents) living in areas of pasture, 29.9%. Animal categories with the highest prevalences also shed the highest average oocyst numbers per gram of faeces (ranging from 1.4 x 10(3) for bull beef to 1.1 x 10(5) for calves). Analysis of annual and seasonal data for each animal category revealed that patterns of infection were variable and sporadic; this means that short-term sampling was never likely to provide a true or representative picture. Seasonally combined data for adult livestock, young livestock and small wild mammals showed all three categories tended to have the highest Cryptosporidium prevalences in the autumn. Calves were separated from their dams within 24h of birth and yet showed high prevalence of infection in most years despite the low prevalence for the dairy herd. It is possible the coincidence of high autumn prevalence in mice with the main period for the rearing of calves contributed to the infection of the latter. The farming estate was used to teach students of agriculture and took pride in good land management and husbandry practices that produced well fed and healthy livestock. The data from this estate may represent, therefore, the baseline, the lowest possible levels to be expected, for Cryptosporidium infection and oocyst production on a lowland farm in the United Kingdom.

Occurrence of Cryptosporidium in agricultural surface waters during an annual farming cycle in lowland UK

A 17-month survey based on weekly testing for Cryptosporidium oocysts in surface waters draining a livestock farm on a Warwickshire (UK) estate has shown that the parasite is present throughout the year, with the highest frequency of occurrence and maximum concentrations during the autumn and winter. The 190 ha farm is managed as an exemplar for a teaching institution. There were up to 800 livestock present at peak times of year in the catchment of the stream draining the estate. Oocysts were concentrated from grab samples by a flocculation procedure, stained with monoclonal antibody and detected by fluorescence microscopy. Overall, 274/418 (66%) of samples were positive for Cryptosporidium. Where the stream passed from the estate, the occurrence was 79%, with mean and median oocysts/l of 0.48 and 0.2, respectively. Highest oocyst levels coincided with calving and increased wild animal numbers following breeding. There was no correlation of oocyst levels with rainfall or slurry spreading. Cryptosporidium was also frequently found in a pond on arable land (no livestock) indicating that wild animals alone contributed oocysts to surface waters. These results from a well managed livestock farm may represent a typical natural baseline for levels of occurrence and concentration of Cryptosporidium oocysts in surface waters of the lowland agricultural environment of the UK.

The Norway rat as a reservoir host of Cryptosporidium parvum

The potential of Norway rats (Rattus norvegicus) to spread the parasite Cryptosporidium parvum was investigated by examining parasite prevalence in relation to the structure and movements of three permanent rat populations living on farmland in Warwickshire (UK) from October 1994 to March 1997. One population lived among a group of farm buildings housing cattle, while the other two had no contact with livestock, one living around a pond and its outflowing stream and the other on a rubbish tip. Overall, parasite occurrence was 24% (n = 438), but it varied according to body weight (age) with 40% of juveniles (< or =100 g) infected decreasing to 12% for adults >400 g, suggesting that actively breeding populations are potentially more likely to spread the parasite than non-breeding populations. There was no difference in prevalence between the three populations. The parasite was detected in more males (29%) than females (19%). Seasonally, on the livestock farm, prevalence was significantly lower in autumn (10%), but varied little (31-36%) from winter to summer. In contrast, on the arable farm, prevalence peaked in summer (50%) with a trough in winter (6%). Infection in rats appeared to last <67 days. Rats living on the livestock farm had home ranges largely confined to the cattle sheds, thereby maintaining a potential source of infection for livestock if rodent control was not part of a decontamination program. Equally, rats living around the pond on the arable farm provided a source of oocysts to contaminate the pond water, as well as being able to carry the parasite to nearby farm buildings or even to neighboring farms.