Identification of priority populations such as men who have sex with men (MSM) is important in surveillance systems to monitor trends of sexually transmitted infections (STIs). We explored using routinely collected non-behavioural data as a means to establish MSM status in surveillance by assessing anorectal swab as a marker of male-to-male sexual exposure. We used chlamydia testing data from a sexual health clinic, 2007–2012. Men reporting any male sexual partner(s) in the previous 12 months were considered MSM. The dataset was split into development and validation samples to develop a univariate predictive model and assess the model fit. The dataset included 30 358 individual men and 48 554 episodes of STI testing; 45% were among reported MSM and an anorectal swab was performed in 40% of testing episodes. Anorectal swabbing had good diagnostic performance as a marker for MSM status (sensitivity = 87%, specificity = 99%, positive predictive value = 98·6%, negative predictive value = 90·3%). The model showed good fit against the internal validation sample (area under the curve = 0·93). Anorectal swabs are a valid marker of MSM behaviour in surveillance data from sexual health clinics, and they are likely to be particularly useful for monitoring STI trends among MSM with higher risk behaviour.

High-precision geochronological techniques have improved in the past decade to the point where volcanic ash beds interstratified with fossil-bearing rocks can be dated to a precision of 0.1% or better. The integration of high-precision U-Pb zircon geochronology with bio/chemo-stratigraphic data brings about new opportunities and challenges toward constructing a fully calibrated time scale for the geologic record, which is necessary for a thorough understanding of the distribution of time and life in Earth history. Successful implementation of geochronology as an integral tool for the paleontologist relies on a basic knowledge of its technical aspects, as well as an ability to properly evaluate and compare geochronologic results from different methods. This paper summarizes the methodology and new improvements in U-Pb zircon geochronology by isotope dilution thermal ionization mass spectrometry, specifically focused on its application to the stratigraphic record.

Two thin volcaniclastic sandstone beds in the Bryn-llin-fawr road section in North Wales overlie an apparent sequence boundary within the uppermost Cambrian Acerocare Zone and are overlain by lowest Ordovician (lower Tremadoc) Rhabdinopora faunas. U–Pb geochronology of zircons from these sandstones yields a maximum Cambrian–Ordovician boundary age of 489±0.6 Ma. This age indicates both that the Tremadoc Series (lowest Ordovician) may be shorter in duration than was previously thought and that the duration of the Middle and Late Cambrian (c. 22 Ma) was much less than that of the Early Cambrian (c. 33 Ma). Cambrian trilobite zones locally had an average duration as short as 1 Ma.