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HIV-1 Incidence Rates and Risk Factors in Agricultural Workers and Dependents in Rural Kenya: 36-Month Follow-Up of the Kericho HIV Cohort Study

Shaffer, Douglas N MD, MHS*†‡; Ngetich, Ignatius K MSc; Bautista, Christian T MS*‖; Sawe, Frederick K MBChB, MMED; Renzullo, Philip O PhD, MPH; Scott, Paul T MD, MPH *‡; Kibaya, Rukia M MSc; Imbuki, Kennedy O MA; Michael, Nelson L MD, PhD *‡; Birx, Deborah L MD *‡#; Wasunna, Monique K MBChB, MSc, PhD, DTM&H§; Robb, Merlin L MD

JAIDS Journal of Acquired Immune Deficiency Syndromes: April 1st, 2010 - Volume 53 - Issue 4 - p 514-521
doi: 10.1097/QAI.0b013e3181bcdae0
Epidemiology and Social Science

Background: Incidence data from prospective cohort studies using rigorous laboratory methods are important in designing and evaluating HIV vaccine and therapeutic clinical trials and health care programs. We report 36-month HIV-1 incidence rates and demographic and psychosocial risks from the Kericho cohort in rural Kenya's southern Rift Valley Province.

Methods: Thirty-six month, prospective, closed, observational cohort study of adult plantation workers and dependents followed biannually. HIV-1 incidence rates per 100 person-years (py) were calculated, and Cox regression analyses were used to estimate hazards ratios (HR) associated with seroconversion.

Results: Two thousand four hundred volunteers (mean age ± SD = 30.1 ± 8.5 years; 36.5% women) participated. Twenty-nine new HIV cases were identified in year 1 of follow-up, which increased to cumulative totals of 49 and 63 cases in years 2 and 3, respectively. The corresponding 1-, 2-, and 3-year incidence rates were 1.41 [95% confidence interval (CI) = 0.95-2.02], 1.16 (95% CI = 0.86-1.54), and 1.00 (95% CI = 0.77-1.28) per 100 py. Risk factors associated with HIV seroconversion included the following: of the Luo tribe (HR = 3.31; 95% CI = 1.65-6.63), marriage more than once (HR = 2.83; 95% CI = 1.20-6.69), self-reported male circumcision (HR = 0.32; 95% CI = 0.17-0.60), history of sexually transmitted infection (HR = 2.40; 95% CI = 1.09-5.26), history of substance abuse during sex (HR = 2.44; 95% CI = 1.16-5.13), and history of transactional sex (HR = 3.30; 95% CI = 1.79-6.09).

Conclusions: HIV-1 incidence rates were relatively low in adult plantation workers and dependents in rural Kenya. Cohorts including higher risk populations (eg, commercial sex workers) warrant consideration for regional HIV preventive vaccine trials. Even low incidence, well-described cohorts generate valuable epidemiological clinical trial data.

From the *US Military HIV Research Program, Rockville, MD, USA; †United States Army Medical Research Unit, Kericho, Kenya; ‡Walter Reed Army Institute of Research, Rockville, MD, USA; §Kenya Medical Research Institute, Kericho and Nairobi, Kenya; ‖Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc, Rockville, MD, USA; ¶Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA; and #D. L. Birx is currently affiliated with the Global AIDS Program, US Centers for Disease Control and Prevention, Atlanta, GA.

Received for publication March 20, 2009; accepted July 31, 2009.

Portions of this manuscript were presented in abstract session by Mr. Ignatius K. Ngetich (# MOP E0234) at the XVII International AIDS Conference, Mexico City, Mexico, 3-8 August 2008.

Supported by The Walter Reed Army Institute of Research Institutional Research Board human use protocol #855 (RV142); “HIV and Malaria Cohort Study Among Plantation Workers and Adult Dependents in Kericho, Kenya,” is funded through the United States Military HIV Research Program (the Walter Reed Army Institute of Research and the Henry M. Jackson Foundation for the Advancement of Military Medicine Inc).

Disclaimer: The views expressed here are the opinions of the authors and are not to be considered as official or reflecting the views of the Walter Reed Army Institute of Research, the US Army, the US Department of Defense; the Kenya Medical Research Institute; the Henry M. Jackson Foundation for the Advancement of Military Medicine Inc; the Division of AIDS, National Institutes of Health; or the Global AIDS Program, US Centers for Disease Control and Prevention.

Correspondence to: Douglas N. Shaffer, MD, MHS, Director, United States Army Medical Research Unit-Kenya/Walter Reed Project HIV Program, Kericho, Kenya (e-mail:

© 2010 Lippincott Williams & Wilkins, Inc.