When researchers looked at who used condoms regularly versus inconsistently, they found couple-related factors like age difference and how steady or casual the relationship was explained more than half of the variation in condom use. Traits of the individuals accounted for 15 percent or less of the variation.
The results suggest a need for a shift in the way individuals are counseled about condom use, according to Dr. Luu Ireland, from the department of obstetrics and gynecology at the University of California, Los Angeles.
"As physicians we focus more on the individual . . . (but based on the study findings) we probably should address more the type of relationship our patients are going to be involved in," Ireland, who was not involved in the study, said in an email to Reuters Health.
Previous research has focused on either the individual factors associated with condom use, such as gender, age and ethnicity, or on partnership factors, such as the duration and exclusivity of the relationship.
In the current study, Amy Matser, of the Public Health Service of Amsterdam, and her team looked at both sets of factors to determine which were most important in predicting who would use condoms regularly.
They surveyed a total 2,144 men and women who visited a sexually transmitted infections (STI) clinic in Amsterdam from May to August 2010. Participants were asked about their sexual behaviors with up to four of their most recent sexual partners - 6,401 partnerships in all - during the previous year.
Half of the study participants were under age 25 and just over half were women, the researchers note in the journal Sexually Transmitted Infections.
They found condoms were used regularly in just 33.5 percent of the 4,014 casual partnerships and 14 percent of the steady partnerships, according to Matser.
Specific characteristics of these couples were most commonly associated with irregular condom use, for example, it became more likely with the increasing duration of relationships, particularly in steady relationships.
Inconsistent condom use was also more frequent when both partners in a couple were the same ethnicity and in couples with increasing number of sex acts, participation in anal sex and sex-related drug use. This was true of both steady and casual sex relationships.
"We found that when partners are more familiar with each other and when they are more alike, inconsistent condom use becomes more prevalent," Matser told Reuters Health in an email. "We should rethink of our current prevention strategies to promote condom use to see whether these methods are sufficiently capable of increasing awareness of the risk of acquiring STIs from partners who are more familiar."
Characteristics of individuals were also linked with condom use, for instance, less-educated men and women were more likely to use condoms inconsistently than those with a university degree. This was particularly true in steady relationships versus casual couplings.
Dutch women and men of non-Dutch ethnicity in steady relationships were also more likely to report inconsistent condom use than their counterparts.
Ireland points out that the authors did not strictly define "inconsistent" condom use. A couple that used condoms 95 percent of the time and a couple that used condoms 5 percent of the time would both be lumped in the same inconsistent use category. Still, she added, "inconsistent condom use and nonuse is really high," according to this study's findings.
The authors acknowledge that since the participants were recruited from visitors to a Dutch STI clinic, an inherently high-risk population, the study results may not be applicable to everyone.
They should hold true in western countries like the U.S. or the UK, according to Matser, "because norms and values in these countries do not differ much from the Netherlands."
Ireland said, anecdotally, the patterns seen in the study population may not be that much different among her own patients in the U.S., noting that people in longer relationships or those who are familiar with their sexual partners may be less likely to use condoms.
"In my experience, people tend to be motivated to use condoms when they feel they are at risk," she said, adding "the only way to be safe is to practice 100 percent condom use."
"If they're not using condoms with you, there's a chance they're not using it with other sexual partners," Ireland said.