FACTORS INFLUENCING BEHAVIOUR CHANGE FOR TH E PREVENTION OF THE SPREAD OF HIV/AIDS AMONG STUDENTS IN GITHUNGURI DIVISION, KIAMBU EAST DISTRICT, KENYA BY NDEGWA ISABEL NJERI REG NO. I57/CE/12138/04 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTERS DEGREE IN PUBLIC HEALTH IN THE SCHOOL OF HEALTH SCIENCES OF KENYATTA UNIVERSITY JANUARY 2011