Samkange-Zeeb et al. BMC Public Health 2011, 11:727 http://www.biomedcentral.com/1471-2458/11/727 and possibly lead to ectopic pregnancies and infertility [8-11]. Female adolescents are likely to have a higher risk of contracting an STD than their male counterparts as their partners are generally older and hence more likely to be infected [2,12]. The declining age of first sexual intercourse has been proffered as one possible explanation for the increase in numbers of STDs [7]. According to data from different European countries, the average age of first sexual inter- course has decreased over the last three decades, with increasing proportions of adolescents reporting sexual activity before the age of 16 years [13-18]. An early onset of sexual activity not only increases the probability of having various sexual partners, it also increases the chances of contracting a sexually transmitted infection [19]. The risk is higher for female adolescents as their cervical anatomic development is incomplete and espe- cially vulnerable to infection by certain sexually trans- mitted pathogens [20-23]. The reluctance of adolescents to use condoms is another possible explanation for the increase in STDs. Some sur- veys of adolescents have reported that condoms were found to be difficult to use for sexually inexperienced, detract from sensual pleasure and also embarrassing to suggest [24-26]. Condoms have also been reported to be used primarily as a protection against pregnancy, not STD, with their use becoming irregular when other contracep- tives are used [15,27]. Furthermore, many adolescents do not perceive themselves to be at risk of contracting an STD [27]. We conducted this systematic review in order to deter- mine awareness and knowledge of school-going adoles- cents in Europe of sexually transmitted diseases, not only concerning HIV/AIDS, but also other STDs such as chla- mydia, gonorrhoea, syphilis and human papillomavirus (HPV). Where possible we will identify differences in awareness and knowledge by key demographic variables such as age and gender, and how awareness has changed over time. Although knowledge and awareness have been reported to have a limited effect on changing attitudes and beha- viour, [16,28-30] they are important components of sex education which help promote informed, healthy choices [31-33]. As schooling in Europe is generally compulsory at least up to the age of 15 years [34] and sex education is part of the school curriculum in almost all European countries, school-going adolescents should be well informed on the health risks associated with sexual activ- ity and on how to protect themselves and others. In view of the decreasing age of sexual debut and the reported increasing numbers of diagnosed STDs among young people, results of our review can help point out areas where STD risk communication for school-attending adolescents needs to be improved. Page 2 of 12 Methods Search strategy We performed literature searches in PubMed using various combinations of the search terms “STD”, “HIV”, “HPV”, “chlamydia”, “syphilis”, “gonorrhoea”, “herpes”, “hepatitis B”, “knowledge”, “awareness”, and “adolescents”. The refer- ence lists of selected publications were perused for further publications of interest. The search was done to include articles published from 01.01.1990 up to 31.12.2010. Inclu- sion and exclusion criteria were specified in advance and documented in a protocol (Additional File 1). Inclusion criteria Studies were selected if they reported on awareness and/or knowledge of one or more sexually transmitted disease(s) among school-attending adolescents in a European coun- try, or in Europe as a whole, and were published in English or German. Exclusion criteria Case reports, reviews, editorials, letters to the editor, expert opinions, studies on sexual activity/behaviour only, studies evaluating intervention programmes and studies not specifically on school-attending adolescents were excluded. Methodological assessment of reviewed studies We used a modified version of the Critical Appraisal Form from the Stanford School of Medicine to assess the metho- dology of the studies included in the review [35]. The stu- dies were classified according to whether or not they fulfilled given criteria such as ‘Were the study outcomes to be measured clearly defined?’, ‘Was the study sample clearly defined?’, or ‘Is it clear how data were collected?’ (Table 1). No points were allocated. Instead, the following categorisations could be selected for each assessment statement: ‘Yes’, ‘Substandard’, ‘No’, ‘Not Clear’, ‘Not Reported’, ‘Partially Reported’, ‘Not Applicable’, ‘Not Possible to Assess’, ‘Partly’. The assessment was done independently by two of the authors (FSZ, LS) who then discussed their findings. Definition of awareness and knowledge For the purpose of this review studies were said to have assessed awareness if participants were merely required to identify an STD from a given list or name an STD in response to an open question. Knowledge assessment was when further questions such as on modes of trans- mission and protection were posed. Results Overall, 465 titles and abstracts were obtained from the searches conducted. Three hundred and ninety-three articles were excluded as they did not report on studies