RESUMEN
This paper develops methods to test for associations between two variables with clustered data using a U-Statistic approach with a second-order approximation to the variance of the parameter estimate for the test statistic. The tests that are presented are for clustered versions of: Pearsons χ 2 test, the Spearman rank correlation and Kendall's τ for continuous data or ordinal data and for alternative measures of Kendall's τ that allow for ties in the data. Shih and Fay use the U-Statistic approach but only consider a first-order approximation. The first-order approximation has inflated significance level in scenarios with small sample sizes. We derive the test statistics using the second-order approximations aiming to improve the type I error rates. The method applies to data where clusters have the same number of measurements for each variable or where one of the variables may be measured once per cluster while the other variable may be measured multiple times. We evaluate the performance of the test statistics through simulation with small sample sizes. The methods are all available in the R package cluscor.
RESUMEN
BACKGROUND: Thailand has made progress in reducing perinatal HIV transmission rates to levels that meet the World Health Organization targets for so-called "elimination" (<2%) of mother-to-child transmission (MTCT). OBJECTIVES: To highlight the Thailand National Guidelines on HIV/AIDS Treatment Prevention Working Group issued a new version of its National Prevention of MTCT guidelines in March 2017 aimed to reduce MTCT rate to <1% by 2020. DISCUSSION OF GUIDELINES: The guidelines include recommending initiation of antepartum antiretroviral therapy (ART) containing tenofovir disoproxil fumarate (TDF) plus lamivudine (3TC)/emtricitabine (FTC) plus efavirenz regardless of CD4 cell count as soon as HIV is diagnosed for ART naïve HIV-infected pregnant women. An alternative regimen is TDF or zidovudine (AZT) plus 3TC/FTC plus lopinavir/ritonavir (LPV/r) for HIV-infected pregnant women suspected resistant to non-nucleoside reverse transcriptase inhibitors. Treatment should be started immediately irrespective of gestational age and continued after delivery for life. Raltegravir is recommended in addition to the ART regimen for HIV-infected pregnant women who present late (gestational age (GA) ≥32 weeks) or those who have a viral load (VL) >1000 copies/mL at GA ≥32 weeks. HIV-infected pregnant women who conceive while receiving ART should continue their treatment regimen during pregnancy. HIV-infected pregnant women who present in labor and are not receiving ART should receive single-dose nevirapine immediately along with oral AZT, and continue ART for life. Infants born to HIV-infected mothers are categorized as high or standard risk for MTCT. High MTCT risk is defined as an infant whose mother has a viral load (VL) > 50 copies/mL at GA > 36 weeks or has received ART <12 weeks before delivery, or has poor ART adherence. These infants should be started on AZT plus 3TC plus NVP for 6 weeks after delivery. Infants with standard MTCT risk should receive AZT for 4 weeks. Formula feeding exclusively is recommended for all HIV-exposed infants.