The most important finding in our study was the low level of basic knowledge regarding STI among the respondents. The average overall knowledge score was as low as 6.5 (of 40 possible correct answers). There were relatively low proportions of women who could correctly answer about suspected symptoms, causes, curability and complications of STI. Urethral discharge in men, an important symptom of STI was neglected by the study respondents, and majority of the women did not report knowledge of any symptom of STI. Meanwhile, the concepts that bad hygiene, sex during menses or soon after delivery, multiple childbirths or abortions are "causes" of STI, and untreated STI can lead to HIV/AIDS also existed among the respondents. These findings are consistent with other qualitative studies in Vietnam showing limited knowledge [15, 18] and misconceptions regarding STI among people in the community [15, 19].
Our study showed a certain number of the study women did not know if STI can be prevented, and a low percentage of women gave correct answers about STI prevention. Condom use is considered the single, most efficient, available means to reduce the sexual transmission of both HIV and STI . Nevertheless, in Vietnam, low knowledge of condom use for STI prevention among the general population has been previously shown . A study in India also shows 22% of young girls do not know about condom use could protect people from STI . Among our respondents however, especially among the unmarried women, this knowledge was even less. Whereas, studies show that 92% of young people in Ho Chi Minh city know that the use of condoms protects against HIV , and that there is existence of adequate knowledge of HIV but little concern for STI among female sex workers . The difference could possibly be due to an unbalanced effort that has been given to the combat against HIV/AIDS since 97.5% of the government funds were allocated for HIV/AIDS prevention and care, while only 2.5% were for STI control activities . This might put people at increased risk because of poor concern for STI. Besides, nearly half of our respondents either did not know the necessity of partner treatment or claimed that it was not necessary. Insufficient knowledge regarding STI prevention and partner treatment among the study women may result in neglecting the risks of unsafe sex.
Studies have shown that in a high-income society, better knowledge is not related to income or residence but related to higher education [28, 29], having ever had sex , and STI history [28, 30]. Being knowledgeable about RTI was related to higher probability of self-reported symptoms has been shown among rural Chinese women . Our results showed that the overall STI knowledge was higher among married women and among those who had had self-reported symptoms during the past six months. Women with low education or low economic status had less knowledge of STI than those with higher education or economic category. Moreover, the results demonstrated an obvious association between low STI knowledge and residency in the mountainous and highland areas. This may reflect the fact that women with low education and from rural or remote areas wait before seeking care for STI . Lack of awareness of STI consequences among our respondents may have led delayed treatment.
In our study, up to one-third of the unmarried women reported no knowledge about STI. Moreover, the women under the age of 20 demonstrated the lowest level of STI knowledge. This may be partially due to the sensitive nature of the issue and feelings of shame among women, especially unmarried women, when talking about STI [15, 18].
To our knowledge, one new finding in our study is the impact of experience of induced abortion, but not of childbirth, on STI knowledge. Those who have experienced an induced abortion might have been provided information, by healthcare providers, about the prevention of unwanted pregnancies, which is associated with STI knowledge. However, women who go to health facilities for childbirth might not receive information about diseases related to sexuality. Thus, how healthcare providers phrase their information may play an important role in improving people's STI knowledge.
Furthermore, the analysis showed that the intra-cluster correlation coefficient was significantly greater than 0 (p < 0.01), which indicated the existence of relations between knowledge levels of women in each cluster. This may be caused by information acquired from peers/friends within the cluster. This could be easily understood by the fact that women having symptoms usually seek help or advice from peers/friends and healthcare providers . Studies in Vietnam and elsewhere show that HIV/AIDS information is derived mainly from friends , healthcare providers , and mass media [20, 24, 32]. Therefore, peer/friend education, informal conversations between women within clusters, mass communication, and the use of healthcare providers as means of providing information to the community should be taken into consideration when designing and implementing intervention programmes.
Since we had no drop-outs, one might question how we obtained such a high response rate. This was probably due to a number of different reasons. Firstly, we have had good cooperation with the households and the commitment of local authorities to the FilaBavi. Secondly, the interviewers were female surveyors of FilaBavi, who have been well-trained in doing household surveys and have created good relationships with households. The face-to-face interview can clarify questions, and usually get high response rates because the presence of the interviewer encourages participation and involvment of participants . Thirdly, the purposes and procedures of the study were clearly explained before the data collection and the married women were eager to participate in the gynaecological examination to be performed by experienced female doctors from Hanoi together with some sophisticated tests and treatment provided free of charge . Lastly, when designing the study and planning for data collection, we deliberately chose the most appropriate time of the year in order to avoid the harvest period and thus facilitate the participation of the study subjects.
According to the pilot study, it was too sensitive and impossible to include questions about respondents' and/or their husbands'/partners' sexual behaviours or risks for STI/HIV. Furthermore, the topic of this study is possibly sensitive for face-to-face interviews and people are reluctant to disclose their sexual behaviours and may be reluctant to express even their knowledge. Besides, respondents might felt that their answers were not anonymous since the surveyors lived in the area and were known to them and would also come back again for the routine data collection of FilaBavi, therefore, they might have been less informative or open. Consequently, our results possibly underestimated women's knowledge about STI, especially unmarried women's, and did not reflect the magnitude of risks that women and their husbands/partners are engaged in. These problems might have been less by using a self-administered questionnaire . Because of the selection of only women, our results are presumably representative of the female part of the population in Bavi district and possibly other rural areas of Vietnam.
Concerning the scoring, the answers were not weighed since we assumed each item equally. Alternative regression models using weighed scores were also performed (results not presented); the outcomes however, did not differ. We considered the interviewer variances had no significant impact on the results as the intra interviewer correlation coefficient was small (ICC = 0.08).