Failure to understand the risk of false-negative HIV test results during the window period results in anxiety. Patients typically want accurate test results as soon as possible while clinicians prefer to wait until the probability of a false-negative is virtually nil. This review summarizes the median window periods for third-generation antibody and fourth-generation HIV tests and provides the probability of a false-negative result for various days post-exposure. Data were extracted from published seroconversion panels. A 10-day eclipse period was used to estimate days from infection to first detection of HIV RNA. Median (interquartile range) days to seroconversion were calculated and probabilities of a false-negative result at various time periods post-exposure are reported. The median (interquartile range) window period for third-generation tests was 22 days (19-25) and 18 days (16-24) for fourth-generation tests. The probability of a false-negative result is 0.01 at 80 days' post-exposure for third-generation tests and at 42 days for fourth-generation tests. The table of probabilities of falsely-negative HIV test results may be useful during pre- and post-test HIV counselling to inform co-decision making regarding the ideal time to test for HIV.

No abstract

No abstract

outh in custody report high-risk drug use and sexual behaviours. 1 The prevalence of HIV in British Columbia youth in custody was assessed in 1994; 2 hepatitis C virus (HCV) prevalence has never been measured. A recent Ontario study found 1/298 (0.4%) of youth in custody had been HCV-infected and no persons identified with HIV. 3 The prevalence of HCV in BC is twice that of Canada. 4 Therefore we sought to determine HCV and HIV prevalence, and factors associated with intravenous drug use (IDU) and sex for trade among youth in BC custody centres. To increase acceptability of testing, a non-invasive sampling method was utilized. Oral fluid testing using OraSure ® had been previously validated for HIV antibody testing, but less evidence was available for HCV. Therefore we assessed the performance of OraSure ® for the detection of HCV and HIV antibodies for prevalence estimations. BC youth in custody are aged 12-19 years with the majority being 16 or 17. The Youth Criminal Justice Act (2003) encourages moderate sentences and alternatives to imprisonment for less serious crimes. Therefore youth have high rates of short-term confinement; the average stay is <30 days for youth in remand and <60 days for those sentenced. BC has the lowest rate of youth custody admissions in Canada, and youth beds in BC declined from 400 in 1996/7 to 135 in 2004/05. METHODS Validation of the OraSure ® Collection Device OraSure ® (Orasure Technologies Inc, Bethlehem, PA) is a non-invasive device for oral mucosal transudate (OMT) specimen collection, preservation and transportation. The device, a cotton-fibre pad treated with hypertonic salt solution to enhance OMT, is placed between the lower gum and cheek for 2 minutes. Two OMT samples (one from each side of the mouth) and a blood sample, to confirm serostatus, were collected from 110 adults (24 HCV mono-infected, 27 HIV mono-infected, 29 HCV/HIV co-infected and 30 non-infected). The OMT was collected and extracted according to the manufacturers instructions. Serum and OMT aliquots were stored at-70°C. HIV tests for serum and OMT were performed using the ADVIA Cen-taur™ HIV 1/O/2 test (Siemens Medical Solutions Diagnostics, Tarrytown, NY). HIV EIA-reactive OMT were confirmed by Genetic Systems™ HIV-1 Western blot (Bio-Rad Laboratories, Montreal, QC). HCV tests for serum and initial OMT were performed using the