A new US study suggests that in 2005 there were 1.1 million new cases of sexually transmitted infections (STIs) among young Californians. These included diseases such as chlamydia, gonorrhea, syphilis, HPV and HIV and accounted for a state-wide direct medical cost exceeding 1 billion dollars, said the authors.

Published in the Californian Journal of Health Promotion the study is the work of researchers from the Center for Research on Adolescent Health and Development at the Public Health Institute (PHI) in Oakland, California.

Dr Petra Jerman, study author and scientist at PHI said these figures constituted an epidemic of which, like an iceberg, only a small part is visible.

“The estimated number of new cases and their associated costs illustrate that the STD epidemic among California youth remains largely hidden,” said Jerman.

Jerman and colleagues said their goal was to estimate the incidence rate and direct medical cost of new cases of sexually transmitted infections (STIs) in young people in each of California’s 58 counties. This should give policy makers and local healthcare providers good quality information to help prevent and control sexually transmitted infections.

The authors used methods developed by the US Centers for Disease Control and Prevention (CDC) to estimate statewide numbers of new incidences of 8 STIs in California in 2005 among people ranging from 15 to 24 years of age.

The 8 types of infection included in the study were: chlamydia, gonorrhea, syphilis, genital herpes, human papillomavirus (HPV), hepatitis B, trichomoniasis, and HIV.

Using national estimates of the average lifetime cost per case of each type of STI, Jerman and her colleagues also worked out their direct medical cost of by county to help local health authorities use information more relevant to their particular area.

The summarized results showed that:

  • In California in 2005, there were 1.1 million estimated cases of STIs in young people.
  • The total direct medical cost of these cases was 1.1 billion dollars.
  • The estimated number of new STI cases ranged from a low of 82 in Alpine and Sierra counties to a high of 360,000 in Los Angeles County.
  • The associated costs ranged from 38 thousand to 390 million dollars respectively.

The most prevalent STI was HPV, human papillomavirus, with an estimated 590,000 cases in young Californians in 2005. The lowest incidence of new cases was in syphilis, for which the researchers estimated there were 380 cases.

The estimation methods were different for each STI the researchers looked at because of the range of sources of information and the types of informed assumptions they had to make in order to tease out and match their precise criteria for age range and the fact they were looking only at sexually trasmitted infections.

For example, take HIV, with an estimated number of 2,900 new cases in 2005. The authors sourced figures from studies using data from the Office of AIDS at the California Department of Health Services. This gave them an estimated range of 6,788 to 8,988 new cases of HIV in California each year. So they took the midpoint of the range (7,888), and with reference to other research papers, assumed that 75 per cent of HIV infections are acquired sexually and that 50 per cent of these are acquired by people under 25.

In their discussion the authors wrote that the most commonly used marker for STIs is the number of cases reported to local health authorities. Backed by their analysis, they argued that this method underestimated their true incidence and the discrepancy is most likely due to incomplete screening of at risk populations, under reporting of infections and failure to confirm through testing that treatments have been effective.

The authors highlighted some limitations of their analysis, including the fact they estimated the geographic distibution of some STIs on the known distribution figures for other STIs. They said this was not unreasonable because population size is the “main determinant of the STI distribution”. However, this does not take into account the fact that some STIs may have different geographic patterns to others. This could introduce a small amount of error in the distribution of the estimated cases of STIs among the different counties.

The authors concluded that:

“These estimates illustrate the widespread and frequently underreported incidence and costs of youth STIs in California and its counties, and provide the foundation for a comprehensive assessment of youth STI prevention needs.”

“Sexually Transmitted Infections Among California Youth: Estimated Incidence and Direct Medical Cost, 2005.”
Petra Jerman, Norman A. Constantine, Carmen R. Nevarez.
Californian Journal of Health Promotion 2007, Volume 5, Issue 3, 80-91.

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Written by: Catharine Paddock