The median age of first sexual initiation (17 years) in this study is slightly higher than previous studies done in other parts of Ethiopia; in Dessie (16.8 years), in Kolladiba (15 years), in Gojam (13.5 years) and in Butajira (16 years) [10–13]. The difference may be explained by the decrease in early marriage which was the main reason for early sexual initiation in rural youths  due to the recently endorsed family law . Another possible explanation could be that AIDS-related campaigns to delay first sexual intercourse may have had an inhibiting effect.
In this study alcohol users were almost four times more at risk to initiate sexual intercourse earlier than those who didn’t use alcohol. This is similar to earlier findings where alcohol users were two times and three times more likely to initiate sexual intercourse earlier that non-users in Dessie town and Butajira town respectively [10, 11].
Youths who are khat users were also found to be seven times more likely to initiate sexual intercourse earlier than their counterparts. The association of khat use with sexual initiation in this study is stronger than the result obtained from other studies in Dessie town and Butajira where khat chewers were three times and two times at higher risk to initiate sexual intercourse earlier than non chewers in Dessie and Butajira respectively [10, 11]. This difference might be due to the fact that our study is conducted in urban areas and the studies conducted in Dessie and Butajira are in rural areas indicating the difference of age at sexual initiation and khat utilization in rural and urban setting. The possible explanation for the association of khat use with sexual initiation in our study could be due to loss of track of mind induced by khat chewing. During the hypo manic phase, chewers may not be capable of rational judgment and they also may not be able to predict the serious consequences of their actions. Thus, the chewers could walk into the most dangerous situations feeling that there is no danger and being unaware of the possible dangers to their lives or well-being, they get motivated to have unplanned and early sexual initiation.
The present study also showed that unemployed youths were almost seven times more at risk to practice early sexual initiation than those who are employed. The higher risk of early sexual initiation among unemployed youths in our study raises our suspicion of the use of alcohol and khat by unemployed youths which predisposed them to have early sexual initiation. This possible explanation is supported by a study in Ethiopia in which the most frequent substance abusers were jobless youths and street children . The 2001 Ministry of Health, Department of Pharmacy report also indicates that substance abuse is exacerbated by lack of employment opportunities and general feelings of hopelessness.
Viewing pornographic materials were not associated with early sexual initiation in this study which contrasts with previous study in Dessie town where youths viewing pornographic materials were 2.9 times more likely to initiate sexual intercourse earlier than their counterparts . This might be due to few numbers of respondents who acknowledged viewing pornographic materials in our study populations or could be under-reporting of viewing pornographic materials because of social desirability bias or recall bias.
In this study the prevalence of Khat use 35 (33.3%) and alcohol use 50(47.6%) is found to be higher among HIV positive youths than their counterparts. This finding is similar with the result obtained from another study in Addis Ababa, where khat use (31.7%) and alcohol use (55.1%) were found to be higher among HIV positives .
Drug abuse has been incriminated as a potential exposure factor to HIV/AIDS by causing loss of inhibition and involvement in risky sexual behaviors such as unprotected sex, multiple sexual partners, prolonged and traumatic sex, and risky injections [17–19]. In this study alcohol users were found to be almost six times more likely to have HIV sero-positive result than non-users of alcohol and this might be due to the fact that alcohol drinking increases sexual desire which might be responsible for their exposure to HIV infection by having unprotected sex and multiple sexual partners. This finding is supported by similar study in Addis Ababa .
Regarding the association of education level with HIV infection in this study, those who do not have education and those who have primary education level were three times more likely to be infected with HIV those whose education level is secondary and above. This is in line with the fact that people that are more knowledgeable could take care of HIV infection, as they easily understood both the transmission and prevention methods. This finding is similar with the result obtained from another study where people with primary education level or bellow were found to be 2.69 times more likely to be infected with HIV compared with those who have education level of secondary and above .
With regard to gender in this study, females were found to be two times more likely to be infected with HIV than males and this finding is supported by a previous study where females were almost three times more likely to be infected with HIV than males . The possible explanation could be that girls are at a much greater risk at early ages because of both biological and cultural factors such as early age at sexual debut, early marriage, sexual abuse and violence.
Using face-to-face interviews for sensitive issues can invite social desirability bias and therefore underestimate sexual activity. Being a case control study recall bias might have been introduced but we have attempted to reduce it by reducing the age interval of the study participants (youths of age between 15–24 years). The study is health facility based and therefore precludes generalization to all youths in Ethiopia indicating a need for further study using a more representative sample of youths in the country. Despite this limitation, the study provides useful information that will inform health service planners to design a strategy for delaying age at first sex and for the prevention of HIV in Ethiopia.