Chlamydia is a common STD caused by infection with the bacterium Chlamydia trachomatis. In addition to infecting the reproductive tract, chlamydial infections can also occur in the rectum, throat, or eyes. It can cause cervicitis in women and urethritis and proctitis in both men and women.

Untreated chlamydia may lead to serious health consequences in women, including pelvic inflammatory disease (PID), tubal factor infertility, ectopic pregnancy, and chronic pelvic pain. Infection with Chlamydia trachomatis increases the likelihood of acquiring or transmitting HIV.

Chlamydia data are displayed in two ways: case counts and rate per 100,000 population.

Case counts show the number of cases (infections) per county and statewide. This does not necessarily correspond to the number of individuals infected in a given year. Because chlamydia is a curable infection, it is possible for someone to be infected, cured, and re-infected (thus a single individual may be counted twice if she or he were infected twice in the same year). Re-infection is common with asymptomatic STDs like chlamydia because partners pass the infection back and forth to each other, not knowing they are infected because they have no symptoms. Displaying case counts shows the distribution of infection based solely on the number of cases. If a county has between 1 and 5 cases of chlamydia in a given year, the specific number is suppressed in these data.

Rate per 100,000 population shows the number of cases divided by the population and multiplied by 100,000. Displaying rates gives one an understanding of disease distribution relative to the population of a given area (e.g., county). This often shows a different picture than case counts. Although county A may have fewer cases than county B, if county A's population is smaller, they have an overall higher disease burden relative to their county's population. Displaying data in this way can show how these infections affect counties with smaller populations. If a county has a case count of 15 or fewer, the rate per 100,000 is not calculated or displayed. Calculating rates based on small case counts can be misleading because changes in case counts by just one or two cases can drastically change the rate. It may make it falsely appear as though disease burden in a particular county is high.

To select multiple counties click on the first county and then while pressing the control key, click on the other counties you wish to include in the selection. Clicking on a blank area outside the map resets the map to its initial state where all counties are selected.

The map suppresses rates when there are only 1 to 14 cases in the selected county or counties.

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