Search Strategy and Selection Criteria
We searched PubMed, Wanfang, Chinese Biomedical Literature Database, and China National Knowledge Infrastructure to acquire relevant papers published from January 2002 to December 2015. The following detail search strategy was used: (HIV, “human immune*”, “acquired immunodeficiency syndrome”, AIDS) and (China, Chinese) and (ART, HAART, “antiretroviral*’’ , CD4 , “CD4 cell count” , “T cell ”). In addition to database searches, we also screened the references of the selected paper to identify any additional articles. No language restrictions were the whole process of database searches. We chose 2002 as the beginning year for database searches because it was the first year of published WHO guidelines for ART.
The studies that (1)focused on Chinese people living with HIV/AIDS; (2) reported a summary measure of CD4+ T cell counts at ART initiation; and (3) published during 2002–2015,were eligible. We excluded reviews, meeting reports and news articles. We excluded studies that did not report original CD4+ T cell counts data, had fewer than 30 participants, or with a pre-specified CD4+ T cell counts range for inclusion. We also excluded the studies that only reported the number or proportion of patients with CD4 cell counts in particular ranges. When one study presented results of multiple years, we treated them as different computed yeas.
Study Selection and Data Extraction
The titles and abstracts of the retrieved papers were carefully screened by two of us (W.M,, Z.H.. ). One author searched the database and deleted the unavailable papers, and then another author checked the accuracy. When disagreements occurred between these two authors, a third author (H.Z.H,) was invited and a seminar was hold to discuss and resolve the disagreements. All data were extracted and filled using a data abstraction form that developed by us. Characteristics of studies (authors, years, design, regions, population), data type, number of intervals, average interval length (years), and CD4+ T cell counts at initiation (cells/µL) were extracted.
Data type was divided according to the sources of data, and the sources of data included the data from national free antiretroviral treatment program (NFATP), the data from prevention of mother-to-child transmission (PMTCT) program, the data from clinical trial, and the data from descriptive study.
The study region was categorized to eastern China, north China, northeast China, northwest China, south-western China, and south-central China. The income level was divided into low income, low-middle income, high-middle income, and high income based on the gross domestic product per individual in 2013 in China[10, 11].
We abstracted the mean CD4 cell counts from every include paper. When the mean value was unavailable, we would reconstruct mean value or use median value. We abstracted the imputed study years using the method described previously by Siedner MJ et al.. We treated the first years of data collection as the imputed year if the last years was unavailable, and we treated 2 years before the publication year as the imputed year when the first and the last years both were unavailable[8].
Quality Assessment
Because of the majority of included study were descriptive epidemiologic studies, we used the Agency of Healthcare Research and Quality (AHRQ) assessment to assess the study quality. The total score of the AHRQ is 11, and the score from 0 to 3 was assessed as low quality, the score from 4 to 7 was assessed as moderate quality, and the score from 8 to 11 was assessed as high quality[12].
Statistical Analysis
Random-effect model was used to estimate the mean CD4+ T cell counts across studies and its 95% CIs because that it is more conservative and provide better estimates with wider confidence[13]. The I2 (and its 95% CIs) and tau-square were used to assess the between-study heterogeneity, and the H2 was used to assess the within-study heterogeneity [14, 15]. The following subgroup analyses were performed: economic level (high income, high-middle income, low-middle income, low income), study regions (eastern China, mid-southern China, northeast China, northern China, northwest China, southwestern China, and multi-regions), imputed year (from 2003 to 2014), years spanned by data collection (0-3 years, 4-5 years, ≥6 years), data type (Chinese NFATP, clinical data, descriptive study, national PMTCT program), populations (children, eldly patients, general population, injection drug users, MSM, pregnant women, and serodiscordant couples), and sample size (≤100 and >100).
Some sensitivity analyses were performed to assess the robustness of the outcome, for example re-performed all primary analyses using fixed effect model, and re-performed all primary analyses after excluding studies with fewer than 50 participants. We also re-performed all primary analyses including studies reporting data that spanned ≤5 years only, because study with long-term data might easily produce bias. We performed all analyses using Stata software (version 13.0).