Estimating AIDS incidence and jack-knife variance from a continuous delay distribution and incomplete data

Relationship between changes in serum levels of keratin 18 and changes in liver histology in children and adults with nonalcoholic fatty liver disease

BACKGROUND & AIMS

Cross-sectional studies have associated serum levels of the keratin 18 (K18) fragment with histologic features of liver in individuals with nonalcoholic fatty liver disease (NAFLD). We investigated the relationship between changes in serum levels of K18 and changes in liver histology in adults and children with NAFLD.

METHODS

We measured levels of K18 in stored serum samples collected at baseline and various time points from 231 adults with nonalcoholic steatohepatitis and 152 children with NAFLD who participated in 2 separate prospective randomized clinical trials. Liver biopsy specimens collected at baseline and week 96 were reviewed centrally.

RESULTS

There were greater decreases in serum levels of K18 in adults with histologic improvement at week 96 than in those without histologic improvement at week 16 (decrease, 193 ± 293 vs 139 ± 467 U/L; P < .001), week 48 (decrease, 232 ± 360 vs 113 ± 425 U/L; P < .001), or week 96 (decrease, 269 ± 368 vs 97 ± 400 U/L; P < .001). There were greater decreases in serum levels of K18 in children with histologic improvements than in those without histologic improvements at week 48 (decrease, 197 ± 467 vs 47 ± 350 U/L; P = .005) and week 96 (decrease, 206 ± 432 vs 2 ± 474 U/L; P < .001). However, reductions in serum levels of K18 were not better than reductions in levels of alanine aminotransferase in identifying adults with histologic improvement (area under the receiver operator characteristic [AUROC], 0.71; 95% confidence interval [CI], 0.63-0.80; vs AUROC, 0.68; 95% CI, 0.61-0.79; P = .34) or children (AUROC, 0.72; 95% CI, 0.63-0.81; vs AUROC, 0.79; 95% CI, 0.70-0.87; P = .42).

CONCLUSIONS

Decreases in serum levels of K18 are associated strongly with improved liver histologies in adults or children with NAFLD. However, reductions in K18 do not perform better than those in alanine aminotransferase level in identifying histologic changes in NAFLD.

Estimation of reporting delay and suicide incidence in Hong Kong

This paper uses a semi-parametric method to examine the reporting delay distribution in suicides in Hong Kong reporting system. The data arise from a rightly truncated situation in which only suicide cases registered before a specific time are known to have occurred; otherwise they are not recorded in the known death files even if they have occurred. It is shown that the poisoning-related suicide deaths have a longer reporting delay than other suicide methods. By modelling the reporting delay function, a Horvitz-Thompson-type estimator is suggested to adjust for reporting delay and to provide a more timely estimate of the suicide incidences for monitoring the suicide problem in Hong Kong. Based on these analyses, we recommended a suitable cut-off date to collect suicide cases occurring in the previous year and reported before this date in Hong Kong.

Estimating HIV incidence using dates of both HIV and AIDS diagnoses

Knowledge of HIV incidence is important to formulate sensible strategies aimed at controlling the HIV/AIDS epidemic. Back-projection is one of the methods for reconstructing the HIV incidence curve from AIDS incidence data. However, because of the low risk of developing AIDS during the first few years after infection, precise estimates of HIV incidence for the recent past are unlikely if we use AIDS incidence data only. As a result there have been recent attempts to use, not only the date of AIDS diagnosis, but also to use the date of their first positive HIV test. The objective of this paper is to incorporate into back-projection the additional information provided by those individuals who have tested HIV positive but have not yet developed AIDS. This adds information on a very large number of other individuals, and provides the hope that the precision of back-projection is improved considerably. The date of a positive HIV test or an AIDS diagnosis of an individual, whichever comes first, is used in a generalized convolution equation for the purpose of back-projection. The method is illustrated by an application to Australian HIV and AIDS data. Study results show that dramatic improvement in precision is gained for estimates of HIV incidence in recent years when both HIV and AIDS diagnosis dates are used on all individuals.