Assortative mixing as a source of bias in epidemiological studies of sexually transmitted infections: the case of smoking and human papillomavirus.

For studies examining risk factors of sexually transmitted infections (STIs), confounding can stem from characteristics of partners of study subjects, and persist after adjustment for the subjects' individual-level characteristics. Two conditions that can result in confounding by the subjects' partners are: (C1) partner choice is assortative by the risk factor examined and, (C2) sexual activity is associated with the risk factor. The objective of this paper is to illustrate the potential impact of the assortativity bias in studies examining STI risk factors, using smoking and human papillomavirus (HPV) as an example. We developed an HPV transmission-dynamic mathematical model in which we nested a cross-sectional study assessing the smoking-HPV association. In our base case, we assumed (1) no effect of smoking on HPV, and (2) conditions C1-C2 hold for smoking (based on empirical data). The assortativity bias caused an overestimation of the odds ratio (OR) in the simulated study after perfect adjustment for the subjects' individual-level characteristics (adjusted OR 1·51 instead of 1·00). The bias was amplified by a lower basic reproductive number (R 0), greater mixing assortativity and stronger association of smoking with sexual activity. Adjustment for characteristics of partners is needed to mitigate assortativity bias.

Infection transmission and chronic disease models in the study of infection-associated cancers.

In the last three decades, the appreciation of the role of infections in cancer aetiology has greatly expanded. Among the 13 million new cancer cases that occurred worldwide in 2008, around 2 million (16%) were attributable to infections. Concurrently, the approach to prevention of infection-related cancers is shifting from cancer control to infection control, for example, vaccination and the detection of infected individuals. In support of this change, the use of infection transmission models has entered the field of infection-related cancer epidemiology. These models are useful to understand the infection transmission processes, to estimate the key parameters that govern the spread of infection, and to project the potential impact of different preventive measures. However, the concepts, terminology, and methods used to study infection transmission are not yet well known in the domain of cancer epidemiology. This review aims to concisely illustrate the main principles of transmission dynamics, the basic structure of infection transmission models, and their use in combination with empirical data. We also briefly summarise models of carcinogenesis and discuss their specificities and possible integration with models of infection natural history.

Active screening at entry for tuberculosis among new immigrants: a systematic review and meta-analysis.

Although there is no evidence that imported tuberculosis increases the incidence of the disease in host countries, the rise in migration worldwide raises concerns regarding the adequacy of surveillance and control of immigrant-associated tuberculosis in low incidence countries. Assessing the performance of screening of immigrants for tuberculosis is key to rationalizing control policies for the detection and management of immigrant-associated tuberculosis. We performed a systematic review and meta-analysis to determine the yield of active screening for tuberculosis among new immigrants at the point of entry. The yield for pulmonary tuberculosis was 3.5 cases per 1,000 screened (95% CI 2.9-4.1; I(2) = 94%); for refugees, asylum seekers and regular immigrants the estimates were 11.9 (95% CI 6.7-17.2; I(2) = 92%), 2.8 (95% CI 2.0-3.7; I(2) = 96%) and 2.7 (95% CI 2.0-3.4; I(2) = 81%), respectively. The yield estimates for immigrants from Europe, Africa and Asia were 2.4 (95% CI 1.3-3.4; I(2) = 51.5%), 6.5 (95% CI 3.2-10.0; I(2) = 62%) and 11.2 (95% CI 6.2-16.1; I(2) = 95%), respectively. These results provide useful data to inform the development of coherent policies and rational screening services for the detection of immigrant-associated tuberculosis.

Predicting tuberculosis treatment outcome in a low-incidence area.

SETTING: Based on the cohort of pulmonary tuberculosis (PTB) cases resident between 2001 and 2005 in the Piedmont region of Italy, this study estimated the effect of selected determinants on the success of standardised short-course chemotherapy (SSCC). OBJECTIVE: To identify predictors of unsuccessful treatment of PTB and to generate a nomogram to assist treating physicians and public health authorities with the identification of cases needing close follow-up. RESULTS: Overall, 1564 cases were identified. Among new cases, predictors of successful treatment outcome were sex (women vs. men, aOR 0.48, 95%CI 0.37-0.63), geographic origin (EU vs. non-EU countries, aOR 0.43, 95%CI 0.31-0.60) and treatment setting (out-patient vs. in-patient services and unknown setting, aOR 0.2, 95%CI 0.16-0.26). Predictors of unsuccessful outcome were long-term residency status (homeless vs. residential, aOR 9.91, 95%CI 4.38-22.38) and age (for each year, aOR 1.02, 95%CI 1.01-1.03). CONCLUSION: Using a limited number of predictors, the authors designed a nomogram predicting the individual probability of unfavourable SSCC. In principle, this approach is generalisable to other settings and the nomogram can be calibrated on local data to ensure appropriate case management and support targeted treatment follow-up.

Impact of immigration and HIV infection on tuberculosis incidence in an area of low tuberculosis prevalence.

The aim of this study is to assess the effects of immigration from countries with a high prevalence of tuberculosis (HPCs), of HIV/AIDS prevalence, and the ageing of the indigenous population, on tuberculosis distribution in a low-prevalence area (LPCs), the Piedmont Region of Italy. Tuberculosis incidence and HIV cases were identified by linking records from the surveillance systems. Overall, 640 tuberculosis cases were identified and crude annual incidence was found to be 17.3/100000. The incidence rate ratio for HIV infection as a risk factor for tuberculosis (11.4 and 51.9 among individuals from HPCs and LPCs respectively) was greater than that for immigration from HPCs (6.7 and 30.9 among HIV+ and HIV- individuals). Immigration accounted for a larger number of incident cases [population attributable risk % (PAR %): 31.8 and 52.8% among HIV+ and HIV- individuals] than did HIV infection (PAR %: 5.4 and 11.1% among individuals from HPCs and LPCs). Efforts should be made to identify and treat young immigrants from HPCs.

Undetected burden of tuberculosis in a low-prevalence area.

SETTING: Under-ascertainment and under-reporting of tuberculosis (TB) hampers surveillance and control. Case detection is improved by record linkage of case registers and under-reporting can be estimated by capture-recapture (CR) analysis. OBJECTIVES: To assess the completeness of the TB registration systems and estimation of TB incidence and under-reporting in the Piedmont Region of Italy in 2001. METHODS: Record linkage of the 'physician notification system', the TB laboratory register and the hospital records register, and subsequent three-sample CR analysis. RESULTS: Record linkage identified 657 TB cases; CR analysis estimated 47 (95%CI 31-71) unrecorded cases. Under-reporting of the 'physician notification system' was estimated at 21% (95%CI 20-23). The overall estimated TB incidence rate was 16.7 cases per 100000 population (95%CI 16.3-17.3), varying according to the subset investigated: 12.7 for individuals from low TB prevalence countries and 214.1 for immigrants from high TB prevalence countries; 13.1 and 25.8 for persons aged < and > or = 60 years, respectively; and 32.1 in Turin, the regional capital and 10.8 in the rest of the region. CONCLUSIONS: When multiple recording systems are available, record linkage and CR analysis can be used to assess TB incidence and the completeness of different registers, contributing to a more accurate surveillance of local TB epidemiology.

Clinical and demographic aspects of extrathoracic tuberculosis: experience of an Italian university hospital.

OBJECTIVE: The decline of tuberculosis in industrialised countries concerns mainly its pulmonary forms. We have analysed all the cases of non-respiratory tuberculosis admitted to our hospital between January 2000 and June 2002, and compared epidemiological, clinical and diagnostic features in our area with those observed in other industrialised countries with high immigration rates. DESIGN: Patients' records were retrospectively analysed for demographic, clinical, laboratory and instrumental data. Delays in the introduction of treatment were also measured. Characteristics of immigrants were compared with those of native-born persons. We also investigated specific features of extrathoracic tuberculosis affecting different body sites. RESULTS: Forty-eight patients were identified, two thirds of whom were from industrialised countries. Age distribution was characteristically bimodal. Vertebral (n = 18) and lymph node (n = 11) tuberculosis were the most frequently detected forms. The therapeutic delay among individuals from industrialised countries was found to be significantly longer than that of their counterparts from developing countries (P = 0.05). CONCLUSION: We hypothesise that the complex and non-standardised diagnostic approach to the different forms of extrathoracic tuberculosis forms and physicians' lack of awareness of the specific risk of each epidemiological group strongly influence the unacceptably long therapeutic delay. Extrathoracic tuberculosis was more neglected in native-born individuals than in immigrants.