Objectives Determine the incidence and prevalence of nasal colonisation of swine veterinarians with S. aureus in the USA, and quantify associations between risks of S. aureus colonisation and infection and exposure to pigs. Methods 1) Cross-sectional survey of swine veterinarians regarding general occupational health and safety. 2) Longitudinal bacteriological testing (nasal swabs) of 68 veterinarians sampled monthly for 18 months for S. aureus and MRSA carriage. Isolates are characterised of using spa typing (eGenomics and Ridom spa servers) and multilocus sequence typing. The veterinarians work in most major pig producing states of across the USA. Concurrent assessment of intensity of pig exposure, occurrence of skin and soft injuries, occurrence of S. aureus infections, and use of PPE is made monthly via survey. Results Across the first 4 months of bacteriological testing, prevalence of both S. aureus (60-70%) and MRSA (7-10%) were above expected levels in the USA population (30%, 3% respectively). Prevalence is significantly higher in veterinarians sampled within 48 hours of pig contact than after longer periods. Three spa types (539/t034 -ST398; 2/t_unknown -ST 5; 1435/t337 -ST9 comprised 65% of all S. aureus isolates from swine veterinarians. The 3 spa/sequence types have been reported as 'livestock associated' MRSA in Europe (ST398), Asia (ST9) and North America (ST5), but the majority of isolates from US veterinarians were methicillin sensitive (MSSA). Although minor skin injuries have been a frequent occurrence (5% cumulative incidence monthly), clinical infections with MRSA or MSSA have not yet been reported. Conclusions Swine veterinarians in the USA are frequently culture positive for S. aureus variants that are common in swine. Many exposure events appear to result in only transient colonisation. To date, risk of clinical S.aureus infection in this group appears to be modest, despite widespread exposure to the organisms and a high incidence of opportunity for infection via skin wounds.
Objectives To describe the method we use to identify temporal associations between events such as changes in legislation and changes in the incidence of work-related ill-health (WRI) using surveillance data and to show some examples applying this method. Methods The Health and occupation reporting network (THOR) collects reports of work-related ill-health from clinical specialists. Previously we have published a method to analyse time trends in the incidence of WRI using a 2 level negative binomial regression model with beta distributed random effects1. The model also controls for calendar time, reporter type (monthly or annual reporter) and first month as a new reporter. One variable that influences reporting to the THOR surveillance scheme is the length of membership time i.e. reporters tend to report fewer cases after longer membership time resulting in an inherent downward trend in incidence. In an attempt to mitigate this effect, alongside other factors affecting trends in reporting that are not directly related to the incidence of WRI, we have employed a segmented interrupted time series design and included statistical interaction terms in the model. Briefly time periods describing the time periods pre and post-event, and groups representing cases and comparators are prospectively defined. Groups are usually defined by occupation and/or suspected agent. Comparisons are made of the estimated change in incidence per reporter according to inclusion or exclusion within a group. Results This method has been applied to estimate the effect of events anticipated to influence the incidence of short latency WRI (e.g. asthma, dermatitis). Examples will be shown. Conclusions THOR data can contribute to the evaluation of the impact of events such as changes in legislation or interventions.
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