Data collection methods for the IDU surveys reported on here were essentially parallel in Ning Ming County and Lang Son Province, with some variation in the community-based subject recruitment strategies used. The availability of large known drug use gathering places and of officially registered IDUs in Lang Son permitted greater use of probability-based methods in Vietnam, while there was more reliance on peer recruitment in China.
Subject recruitment – China
In Ning Ming County, a modified snowball/peer recruitment technique was used. The project peer educators sent recruiting letters to IDUs they knew personally, inviting them to come to a project center and participate in the survey. The IDUs who came to project centers for interviews were encouraged to recruit 2–3 additional participants. The research participants received 20 Chinese yuan (approximately $2.50) for the interview, 5 yuan for each additional male respondent recruited, and 10 yuan for each additional woman respondent recruited. The eligibility criteria were a minimum of 18 years of age and recent (in the past 6 months) drug injection.
Subject recruitment – Vietnam
Approximately one-half of the sample was based on individuals initially selected from the lists of known IDUs in the project sites. The other half was based on participants initially selected from IDUs present at gathering or shooting places mapped by project staff as part of the initial project implementation. For the half of the sample based initially on registered lists, 10 clusters of 25 individuals each were selected by probability proportional to size (PPS) from the lists of IDUs in each commune. Then four IDUs were picked at random from each selected cluster and these referred others until the quota for the commune was reached.
For the portion of the sample selected initially at IDU gathering or shooting places, sample quotas for these places were determined by PPS based on the numbers of individuals observed at these places during the mapping phase. The interview team then revisited the selected places and chose four individuals at random from among those present at each place at that time (who were not necessarily those present during the mapping phase).
The Vietnamese participants were paid 30,000 Vietnamese dong (approximately US$2) for participating in the interview and HIV test.
Informed consent
In Vietnam, an oral informed consent was obtained for participation in the study, with the interviewer certifying that oral consent had been obtained. This procedure was requested by the Institutional Review Board of the National AIDS Standing Bureau in order to provide more assurance of confidentiality to prospective participants. In China, standard signed informed consents were obtained from all participants. Unique codes were constructed for each participant based on numeric date of birth and several letters representing, for example, the first letter of the mother's family name. (Construction of the record number was slightly different in the two countries.) The objective was to have a unique identifier that the participant could readily reconstruct if he or she lost the project participation card.
Questionnaire
A structured instrument was used for the interviews, based on version 2b of the questionnaire being used in the World Health Organization's Drug Injection Study, Phase II [8]. Trained interviewers, primarily staff of the local health departments, conducted the interviews. The questionnaire covered demographics, drug use, injection and sexual risk behavior, HIV testing history, HIV and hepatitis knowledge, and cross-border travel patterns. A question on the number of times the subject had crossed the border in the 6 months prior to the interview was included.
There are many factors which could influence the "ease/difficulty" in crossing an international border, including distance to the border, cost of transportation, time needed to reach the border, and the need to have official papers for crossing. It was not practical to measure all such factors. Instead, used simple physical distance (in kilometers) to the nearest border point. This gave five distance categories in Vietnam and three distance categories in China.
The baseline survey was conducted in July 2002 in Vietnam and between July and September 2002 in China.
HIV testing
The survey included HIV antibody testing. Participants were given pre-test counseling and post-test counseling at local health centers. Blood was drawn at the time of the interviews by trained phlebotomists from local health departments. Participants were given a card with their unique identifier and returned to the local health center to receive their test results using this identification number. Indeed, they could only retrieve their results by using this number since blood samples were not otherwise labeled. In China, testing was by double ELISA (Vironostika HIV- Uni-form, Organon (Holland)) with confirmation of initial HIV-positive results by Western Blot (Genelabs Diagnostics). All testing was conducted at the laboratory of the Guangxi Center for HIV/AIDS Prevention and Control in Nanning. In Vietnam, testing was performed at the laboratory of the Lang Son Provincial Health Services using the Serodia SFD screening test (Biorad {France}) and double ELISA (Genescreen, Biorad (France); Vironostika, Organon [9]). This is the official protocol of the Ministry of Health in Vietnam and the Lang Son laboratory is authorized to provide HIV testing according to this protocol by the Ministry of Health.
Data analysis
Data were entered and data sets were prepared in EpiInfo, version 6.04 by staff of the Guangxi Center for HIV/AIDS Prevention and Control and the National AIDS Standing Bureau of Vietnam (which has since been merged into the General Department of Preventive Medicine and HIV/AIDS Control of the Ministry of Health). The data were analyzed at Beth Israel Medical Center and Abt Associates Inc. using the Statistical Analysis System, Version 8.2 (SAS, Inc., Cary, NC). Chi square tests were used to assess bivariate relationships among categorical variables. Multi-collinearity problems precluded multivariate analyses.
Ethical review
The study was reviewed and approved by the institutional review boards (IRBs) of the following institutions: Guangxi Center for HIV/AIDS Prevention and Control, the National AIDS Standing Bureau of Vietnam, Abt Associates Inc., and Beth Israel Medical Center.