Chlamydia 2001

View ISDH's basic facts on sexually transmitted diseases (STD)

View CDC's Chlamydia in the United States page

Rates presented are per 100,000 population and are based on the 2000 U.S. Census.

  Cases Incidence
Rate
Total 15,294 251.5
Race-specific cases and rates1
White  5,530 104.0
Black 6,328 1240.7
Other2   595 237.6
Sex-specific cases and rates3
Female 11,699 377.6
Male 3,560 119.4

In 2001, the Indiana State Department of Health (ISDH) received 15,294 reports of patients testing positive for Chlamydia trachomatis, the causative agent of chlamydia.  Of all the reportable diseases in Indiana, chlamydia is the most commonly reported.  The number of reported cases exceeded that of any previous year and was 9.4% greater than the number of reported cases in 2000. 

The incidence rate of chlamydia was 251.5 cases per 100,000 population.  The 2001 incidence rate is slightly inflated because the denominator used for these rates was the total number of residents as determined by Census 2000 and does not reflect the increase of the population between 2000 and 2001.  However, the trend of increasing incidence during the period 1997-2001 is clear (Figure Chl1).  Comparing the total number of cases reported in 2001 to 1997 (9,979), an increase of 53.3% was observed. Inter-year differences ranged from 5.5% (1998-1999) to 17.7% (1999-2000).

This increasing trend reflects endemic chlamydia in the presence of improved ascertainment of cases through time. Increasingly economical and sensitive diagnostic methods were employed through the late 1990's. Additionally, ISDH-funded screening sites have been added in recent years, resulting in more testing among young women. Steadily increasing incidence, therefore, does not necessarily reflect increasing propagation of this pathogen among Hoosiers. Rather, sensitivity of the surveillance system is increasing in response to expanded screening of those at risk. 

Women are overrepresented among those diagnosed with chlamydia.  Known female infections (11,699) exceeded those among males (3,560) by over three-fold.  Chlamydia screening programs preferentially test females, because untreated infections cause reproductive sequelae.  Pelvic inflammatory disease, a substantial proportion of which is caused by infection with C. trachomatis, is the primary cause of preventable infertility.  Federally funded efforts of the Indiana STD Program and the Indiana Family Health Council resulted in selective screening of at-risk young women.  Further, male chlamydia infections are often diagnosed as non-gonococcal urethritis, which is not reportable.  Because these men do not receive pathogen-specific testing, chlamydia morbidity among males is understated. Therefore, the difference between genders reflects a difference in screening practices rather than greater prevalence among females. 

Blacks are overrepresented with respect to this racial group’s contribution to Indiana's total population. While just 8.4% of Indiana’s population was classified as black in the year 2000, over 41% of 2001’s chlamydia cases were reported among this racial group. The race-specific rate for blacks (1240.7) greatly exceeded the race-specific rate for whites (104.0).  This racial disparity may be attributable to higher infection rates among people of color, a greater proportion of this subpopulation having received tests in comparison to their white counterparts, underreporting by providers serving non-black patients, or other factors.

Consistent with previous years’ distribution by age, the preponderance of cases was among adolescents and young adults (Figure Chl2).  In 2001, over 88% of reported cases were among those ages 10-29. The age-group-specific rate for those ages 10-19 was 655.8 per 100,000, while the rate among those ages 20-29 was 910.4 per 100,000. 

The three counties with the greatest number of reported cases were Marion (6,542), Lake (1,085), and St. Joseph (931). Marion County cases far exceeded the number reported from any other jurisdiction within Indiana (Figure Chl3 and Table Chl1). While just 14.2% of Indiana's population resides in Marion County, 42.8% of Indiana's reported chlamydia cases were found among Marion County residents.  Adjusting for population size, Marion County had the highest incidence rate (760.3), followed by Delaware County (370.5), and St. Joseph County (350.6). Figure Chl3 shows the rates for Indiana counties. 

Table Chl1: Chlamydia - Reported Cases by County, Indiana, 2001

Chlamydia - Reported Cases by County
Indiana, 2001
County Number of 
Reported Cases
Incidence Rate per 
100,000 Population
Adams 22 65.4
Allen 1,006 303.2
Bartholomew 156 218.4
Benton 8 84.9*
Blackford 7 49.8*
Boone 35 75.9
Brown 6 40.1*
Carroll 13 64.5*
Cass 52 127.1
Clark 126 130.6
Clay 42 158.2
Clinton 39 115.2
Crawford 11 102.4*
Daviess 11 36.9*
Dearborn 42 91.1
Decatur 23 93.7
DeKalb 28 69.5
Delaware 440 370.5
Dubois 23 58.0
Elkhart 523 286.1
Fayette 39 152.4
Floyd 121 170.9
Fountain 22 122.5
Franklin 8 36.1*
Fulton 12 58.5*
Gibson 17 52.3*
Grant 106 144.4
Greene 24 72.4
Hamilton 99 54.2
Hancock 55 99.3
Harrison 29 84.5
Hendricks 87 83.6
Henry 51 105.1
Howard 128 150.7
Huntington 28 73.5
Jackson 71 171.8
Jasper 17 56.6*
Jay 28 128.4
Jefferson 43 135.6
Jennings 48 174.2
Johnson 134 116.3
Knox 68 173.2
Kosciusko 38 51.3
LaGrange 13 37.2*
Lake 1,085 223.9
LaPorte 283 257.0
Lawrence 47 102.4
Madison 263 197.2
Marion 6,542 760.3
Marshall 41 90.9
Miami 23 63.7
Monroe 271 224.8
Montgomery 34 90.4
Morgan 69 103.5
Noble 44 95.1
Orange 15 77.7*
Owen 24 110.2
Parke 12 69.6*
Perry 17 90.0*
Pike 8 62.3*
Porter 124 84.5
Posey 20 73.9
Pulaski 6 43.6*
Putnam 40 111.1
Randolph 30 109.5
Ripley 23 86.7
Rush 30 164.3
Saint Joseph 931 350.6
Scott 36 156.8
Shelby 64 147.3
Spencer 15 73.6*
Starke 15 63.7*
Steuben 17 51.2*
Sullivan 16 73.6*
Tippecanoe 221 148.4
Tipton 5 30.2*
Union 5 68.0*
Vanderburgh 462 268.7
Vermillion 14 83.4*
Vigo 241 227.7
Wabash 30 85.8
Warren 5 59.4
Warrick 44 84.0
Washington 18 66.1
Wayne 107 150.5
Wells 10 36.2
White 18 71.2
Whitley 22 71.6
Source: Indiana State Department of Health
Note: Rates based on 2000 U.S. Census population.  All other counties had fewer than 
5 cases and are not reported to protect case confidentiality.  County was unknown for 38
of the reported cases.
* Rate based on less than 20 cases and should be considered unstable.
 

Footnotes

1 - Race was unknown for 2,841 of the reported cases.

2 - "Other" includes American Indian/Alaska Native, Asian, Native Hawaiian/Pacific Islander, and multiracial. 

3 - Sex was unknown for 35 of the reported cases.

* - Rate based on less than 20 cases and should be considered unstable.