Incidence estimation using a single cross-sectional age-specific prevalence survey with differential mortality.

Here, we present a method for incidence estimation of a curable, non-recurring disease when data from a single cross-sectional survey are used together with population-level mortality rates and an assumption of differential mortality of diseased versus non-diseased individuals. The motivating example is cataract, and the VISION2020 goal to eliminate avoidable blindness globally by 2020. Reliable estimates of current and future cataract disease burden are required to predict how many surgeries would need to be performed to meet the VISION2020 goals. However, incidence estimates, needed to derive future burden, are not as easily available, due to the cost of conducting cohort studies. Disease is defined at the person-level in accordance with the WHO person-level definition of blindness. An extension of the standard time homogeneous illness-death model to a four-state model is described, which allows the disease to be cured, whereby surgery is performed on at least one diseased eye. Incidence is estimated, and the four-state model is used to predict disease burden assuming different surgical strategies whilst accounting for the competing risk of death. The method is applied to data from approximately 10,000 people from a survey of visual impairment in Nigeria.

Risk of paediatric multisystem inflammatory syndrome (PIMS-TS) during the SARS-CoV-2 alpha and delta variant waves: National observational and modelling study, 2020-21, England.

Objectives: Paediatric Multisystem Inflammatory Syndrome (PIMS-TS) is a rare life-threatening complication that typically occurs several weeks after SARS-CoV-2 infection in children and young people (CYP). We used national and regional-level data from the COVID-19 pandemic waves in England to develop a model to predict PIMS-TS cases. Methods: SARS-CoV-2 infections in CYP aged 0-15 years in England were estimated using the PHE-Cambridge real-time model. PIMS-TS cases were identified through the British Paediatric Surveillance Unit during (March-June 2020) and through Secondary Uses Services (SUS) from November 2020. A predictive model was developed to estimate PIMS-TS risk and lag times after SARS-CoV-2 infections. Results: During the Alpha wave, the model accurately predicted PIMS-TS cases (506 vs. 502 observed cases), with a median estimated risk of 0.038% (IQR, 0.037-0.041%) of paediatric SARS-CoV-2 infections. For the Delta wave, the median risk of PIMS-TS was significantly lower at 0.026% (IQR, 0.025-0.029%), with 212 observed PIMS-TS cases compared to 450 predicted by the model. Conclusions: The model accurately predicted national and regional PIMS-TS cases in CYP during the Alpha wave. PIMS-TS cases were 53% lower than predicted during the Delta wave. Further studies are needed to understand the mechanisms of the observed lower risk with the Delta variant.

The natural history of Chlamydia trachomatis infection in women: a multi-parameter evidence synthesis.

BACKGROUND AND OBJECTIVES: The evidence base supporting the National Chlamydia Screening Programme, initiated in 2003, has been questioned repeatedly, with little consensus on modelling assumptions, parameter values or evidence sources to be used in cost-effectiveness analyses. The purpose of this project was to assemble all available evidence on the prevalence and incidence of Chlamydia trachomatis (CT) in the UK and its sequelae, pelvic inflammatory disease (PID), ectopic pregnancy (EP) and tubal factor infertility (TFI) to review the evidence base in its entirety, assess its consistency and, if possible, arrive at a coherent set of estimates consistent with all the evidence. METHODS: Evidence was identified using 'high-yield' strategies. Bayesian Multi-Parameter Evidence Synthesis models were constructed for separate subparts of the clinical and population epidemiology of CT. Where possible, different types of data sources were statistically combined to derive coherent estimates. Where evidence was inconsistent, evidence sources were re-interpreted and new estimates derived on a post-hoc basis. RESULTS: An internally coherent set of estimates was generated, consistent with a multifaceted evidence base, fertility surveys and routine UK statistics on PID and EP. Among the key findings were that the risk of PID (symptomatic or asymptomatic) following an untreated CT infection is 17.1% [95% credible interval (CrI) 6% to 29%] and the risk of salpingitis is 7.3% (95% CrI 2.2% to 14.0%). In women aged 16-24 years, screened at annual intervals, at best, 61% (95% CrI 55% to 67%) of CT-related PID and 22% (95% CrI 7% to 43%) of all PID could be directly prevented. For women aged 16-44 years, the proportions of PID, EP and TFI that are attributable to CT are estimated to be 20% (95% CrI 6% to 38%), 4.9% (95% CrI 1.2% to 12%) and 29% (95% CrI 9% to 56%), respectively. The prevalence of TFI in the UK in women at the end of their reproductive lives is 1.1%: this is consistent with all PID carrying a relatively high risk of reproductive damage, whether diagnosed or not. Every 1000 CT infections in women aged 16-44 years, on average, gives rise to approximately 171 episodes of PID and 73 of salpingitis, 2.0 EPs and 5.1 women with TFI at age 44 years. CONCLUSIONS AND RESEARCH RECOMMENDATIONS: The study establishes a set of interpretations of the major studies and study designs, under which a coherent set of estimates can be generated. CT is a significant cause of PID and TFI. CT screening is of benefit to the individual, but detection and treatment of incident infection may be more beneficial. Women with lower abdominal pain need better advice on when to seek early medical attention to avoid risk of reproductive damage. The study provides new insights into the reproductive risks of PID and the role of CT. Further research is required on the proportions of PID, EP and TFI attributable to CT to confirm predictions made in this report, and to improve the precision of key estimates. The cost-effectiveness of screening should be re-evaluated using the findings of this report. FUNDING: The Medical Research Council grant G0801947.

Risk of HIV and Hepatitis B and C Over Time Among Men Who Inject Image and Performance Enhancing Drugs in England and Wales: Results From Cross-Sectional Prevalence Surveys, 1992-2013.

BACKGROUND: Infection risks among people who inject drugs (PWID) are widely recognized, but few studies have focused on image and performance enhancing drugs (IPEDs). Globally, concern about IPED injection has increased and, in the United Kingdom, IPED injectors have become the largest group using Needle and Syringe Programmes. Blood-borne virus prevalence trends among IPED injectors are explored. METHOD: Data from 2 surveys of IPED injectors (2010-2011; 2012-2013) and the national bio-behavioral surveillance system for PWID (1992-1997; 1998-2003; 2004-2009) were merged. Psychoactive drug injectors and women were excluded. Logistic regression analyses explored temporal changes. RESULTS: Between 1992 and 2009, median age increased from 25 to 29 years (N = 1296), years injecting from 2 to 4. There were 53 men who had sex with men (MSM). Overall, 0.93% had HIV, 4.4% ever had hepatitis B (HBV), and 3.9% hepatitis C (HCV, from 1998, N = 1083). In multivariable analyses, HIV increased in 2004-2009 [adjusted odds ratio (AOR) = 10 (95% confidence interval (CI): 0.94 to 106) vs. 1992-2003], and remained elevated (AOR = 4.12, 95% CI: 0.31 to 54, 2012-2013); HBV also increased in 2004-2009 (AOR = 3.98, 95% CI: 1.59 to 9.97). HCV prevalence increase was only borderline significant (AOR = 2.47, 95% CI: 0.90 to 6.77, 2010-2011). HIV and HBV were associated with MSM and HCV with sharing needles/syringes. Uptake of diagnostic testing for HIV and HCV, and HBV vaccination increased (to 43%, 32% and 44% respectively). Condom use was consistently poor; needle/syringe sharing occurred. CONCLUSION: Blood-borne virus prevalences among IPED injectors have increased and for HIV, is now similar to that among psychoactive drug injectors. Targeted interventions to reduce risks are indicated.