Estimating the impact of vaccination using age-time-dependent incidence rates of hepatitis B

The objective of this study was to model the age-time-dependent incidence of hepatitis B while estimating the impact of vaccination. While stochastic models/time-series have been used before to model hepatitis B cases in the absence of knowledge on the number of susceptibles, this paper proposed using a method that fits into the generalized additive model framework. Generalized additive models with penalized regression splines are used to exploit the underlying continuity of both age and time in a flexible non-parametric way. Based on a unique case notification dataset, we have shown that the implemented immunization programme in Bulgaria resulted in a significant decrease in incidence for infants in their first year of life with 82% (79-84%). Moreover, we have shown that conditional on an assumed baseline susceptibility percentage, a smooth force-of-infection profile can be obtained from which two local maxima were observed at ages 9 and 24 years.

On the Use of Historical Control Data in Pre-Clinical Safety Studies

A number of methods to formally incorporate historical control information in pre-clinical safety evaluation studies have been proposed in literature. However, it remains unclear when one should use historical data. Focusing on the logistic-normal model, we investigate situations where historical studies may prove to be useful. Aspects of estimation (precision and bias) and testing (power) for treatment effect are investigated under different conditions such as the number of historical control studies, the degree of homogeneity amongst them, the level of treatment effect and different control rates. The possibility to use a selected subset of historical control studies is also explored.

Model selection for incomplete and design-based samples

The Akaike information criterion, AIC, is one of the most frequently used methods to select one or a few good, optimal regression models from a set of candidate models. In case the sample is incomplete, the naive use of this criterion on the so-called complete cases can lead to the selection of poor or inappropriate models. A similar problem occurs when a sample based on a design with unequal selection probabilities, is treated as a simple random sample. In this paper, we consider a modification of AIC, based on reweighing the sample in analogy with the weighted Horvitz-Thompson estimates. It is shown that this weighted AIC-criterion provides better model choices for both incomplete and design-based samples. The use of the weighted AIC-criterion is illustrated on data from the Belgian Health Interview Survey, which motivated this research. Simulations show its performance in a variety of settings.

Techniques for the placement of hepatic artery catheters for regional chemotherapy in unresectable liver metastases

AIMS

For patients with unresectable liver metastases from colorectal cancer (CRC), hepatic artery infusion chemotherapy (HAIC) can produce higher response rates as compared to systemic chemotherapy. However, the added morbidity and early dysfunction after catheter placement have negatively influenced the outcomes of randomized studies.

METHODS

Between July 1998 and March 2006, 29 patients with unresectable liver metastases from CRC were included in three different HAIC protocols. A catheter was laparoscopically placed in the gastroduodenal artery, retrograde to the common hepatic artery and was attached to a subcutaneous access port. Perioperative parameters and catheter-associated adverse events during chemotherapy were studied.

RESULTS

Mean operating time was 106+/-29 min and median duration of hospitalization was 2 days (range: 1-13). No major perioperative complications occurred but there was 1 death (3.6%) 1 week after surgery due to hemorrhagic shock after necrosis and rupture of the hepatic artery. During a median follow-up of 10 months (range: 0-35) we observed 5 (17%) catheter-associated adverse events, but in only 2 patients (7%) this resulted in a loss of catheter function before the end of chemotherapy. Overall median duration of HAIC was 8 months (range: 1-28).

CONCLUSION

Laparoscopic placement of a hepatic artery catheter is associated with a low operative morbidity. The observed functionality of the hepatic artery ports in our series is encouraging for the use in future studies of HAIC.

Modelling age-dependent force of infection from prevalence data using fractional polynomials

The force of infection is one of the primary epidemiological parameters of infectious diseases. For many infectious diseases it is assumed that the force of infection is age-dependent. Although the force of infection can be estimated directly from a follow up study, it is much more common to have cross-sectional seroprevalence data from which the prevalence and the force of infection can be estimated. In this paper, we propose to model the force of infection within the framework of fractional polynomials. We discuss several parametric examples from the literature and show that all of these examples can be expressed as special cases of fractional polynomial models. We illustrate the method on five seroprevalence samples, two of Hepatitis A, and one of Rubella, Mumps and Varicella.

Evidence for a substantial role of sharing of injecting paraphernalia other than syringes/needles to the spread of hepatitis C among injecting drug users

In industrialized countries, transmission of hepatitis C occurs primarily through injecting drug use. Transmission of hepatitis C in injecting drug users is mainly associated with the sharing of contaminated syringes/needles, although evidence for risk of hepatitis C infection through sharing of other injecting paraphernalia is increasing. In this paper, the independent effects of sharing paraphernalia other than syringes/needles have been estimated. The prevalence and force of infection were modelled using three serological data sets from drug users in three centres in Belgium as a function of the sharing behaviour. It was found that sharing of materials other than syringes/needles indeed seemed to contribute substantially to the spread of hepatitis C among injecting drug users.

Social mixing patterns for transmission models of close contact infections: exploring self-evaluation and diary-based data collection through a web-based interface

Although mixing patterns are crucial in dynamic transmission models of close contact infections, they are largely estimated by intuition. Using a convenience sample (n=73), we tested self-evaluation and prospective diary surveys with a web-based interface, in order to obtain social contact data. The number of recorded contacts was significantly (P<0.01) greater on workdays (18.1) vs. weekend days (12.3) for conversations, and vice versa for touching (5.4 and 7.2 respectively). Mixing was highly assortative with age for both (adults contacting other adults vs. 0- to 5-year-olds, odds ratio 8.9-10.8). Respondents shared a closed environment significantly more often with >20 other adults than with >20 children. The difference in number of contacts per day was non-significant between self-evaluation and diary (P=0.619 for conversations, P=0.125 for touching). We conclude that self-evaluation could yield similar results to diary surveys for general or very recent mixing information. More detailed data could be collected by diary, at little effort to respondents.

Risk factors for bovine herpesvirus-1 seropositivity

This paper reports the investigation of risk factors for bovine herpesvirus-1-seropositivity, based on a cluster-sample survey of the Belgian cattle population. This serosurvey was carried out in 1998 in 309 randomly selected unvaccinated herds of all types (dairy, mixed and beef) were all bovids (N = 11,284) were sampled. Older and male cattle had higher seroprevalence. Origin (homebred or purchased) and herd size interacted; for smaller herds (< or = 50 cattle on the premises), purchase status and larger herd size were risk factors, whereas these effects were not observed for larger herds.

A tree based lack-of-fit test for multiple logistic regression

Several omnibus tests have been developed to assess the fit of a regression model. But many of these lack-of-fit tests focus on the simple regression setting. Here, we focus on multiple logistic regression. Pearson's well-known chi-square test statistic and the deviance statistic are no longer valid in the case that the model contains one or more continuous covariates. To overcome this difficulty, Hosmer and Lemeshow proposed a Pearson type statistic based on groups defined by the so-called deciles of risk. We propose a test statistic that is similar in approach to the Hosmer and Lemeshow statistic in that the observations are classified into distinct groups. In the procedure proposed here however, the grouping is not according to probabilities fitted under the null model. We use a recursive partitioning algorithm to divide the sample space into different groups. This generally allows for a more powerful assessment of the model fit. Simulations are carried out to compare the results of the proposed test to that of Hosmer and Lemeshow. Three data examples illustrate the performance of the tree based lack-of-fit test, in comparison to several other tests.

Hepatitis B in St Petersburg, Russia (1994-1999): incidence, prevalence and force of infection

Hepatitis B (HB) is thought to be an expanding health problem in Russia. The incidence of infection was estimated from mandatorily reported HB cases in St Petersburg. The two-sided t-test for independent samples and the LOESS (locally-weighted regression) smoother were used to compare the age at infection for symptomatic, asymptomatic and chronic infections, by gender. The force of infection was estimated from seroprevalence data (907 sera taken in 1999) using a newly developed nonparametric method based on local polynomials, as well as an earlier method based on isotonic regression and kernel smoothers. With the local polynomial method, pointwise confidence intervals (95%) were constructed by bootstrapping. On average, men contracted HB infection at a significantly younger age than women (in 1999, 21.8 vs 22.7 years, respectively). The overall male to female ratio was 1.92. In 1999 the overall incidence almost doubled compared with the preceding years and tripled among the age groups with highest incidence (15-29-year olds: 85% of cases in 1999). The incidence increase was associated with a lower average age at infection (24.1 years in 1994 vs 22.1 years in 1999). The age and gender-specific force of infection estimates generally confirmed the incidence estimates and emphasized the usefulness of local polynomials to do this. Hence HB transmission in St Petersburg occurs mainly in young adults. The dramatic increase of infections in 1999 was probably due to injecting drug use. Without intervention, HB virus is expected to continue to spread rapidly with a greater proportion of female infections caused by sexual transmission. These trends may also provide an indication for HIV transmission.

Chest pain in general practice or in the hospital emergency department: is it the same?

OBJECTIVE

The aim of the present study was to provide a description of the impact of setting on the diagnostic case mix that is identified in consecutive patients presenting with chest pain.

METHODS

A cross-sectional study was carried out of patients presenting with chest pain according to setting: general practice, self-referred, referred or arriving by ambulance at the hospital emergency department (ED). GPs from 25 general practices situated in the Flemish part of Belgium were recruited, and the hospital involved was a major teaching hospital in the same area. A total of 320 patients in general practice and 580 patients in the hospital ED were studied. The difference in prevalence rates for the major diagnostic categories was the main outcome measure.

RESULTS

Gastrointestinal disorders, musculoskeletal problems and psychopathology are identified more frequently in general practice; and serious lung diseases and cardiovascular diseases in the hospital ED. Within the hospital, there is a strong trend towards increasing frequency of serious cardiovascular diseases including unstable angina (P = 0.01) from self-referred to referred patients and those rushed in by ambulance. The opposite trend was identified for respiratory (P = 0.02) and musculoskeletal (P = 0.07) diseases. The diagnostic case mix in self-referred patients tends to be more similar to the other groups of hospital patients than to patients in general practice.

CONCLUSIONS

There is a large difference between the diagnostic case mix presented in general practice compared with the ED and among referral-related subgroups within the hospital emergency department.

Naegleria australiensis: experimental meningoencephalitis in mice

Naegleria australiensis was recently described as a new species of free-living amoeba pathogenic for mice. Infections of human brain by the free-living amoebae N. fowleri and Acanthamoeba spp. are well known. We here describe the clinicopathological features of experimental infection of the central nervous system of mice by N. australiensis. Weanling mice were inoculated intranasally and intracerebrally. The involvement of the nasal mucosa, olfactory neuroepithelium and lobes, cerebrum and cerebellum was detected in haematoxylin-eosin stained paraffin-embedded sections. Amoebic trophozoites sparsely located throughout the central nervous system were shown better by the immunoperoxidase method. Cysts were not detected. The histopathological changes differ from those produced by N. fowleri, especially in the degree of severity. They may be confused with those caused by Acanthamoeba spp. which usually produced subacute and chronic encephalitis with a prolonged clinical course.