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8 Sexually Transmitted Infection Incidence

 Indicator undergoing revision

Description | Specific Indicators | Corresponding Mandatory Objectives | Corresponding Indicators from Other Sources | Data Sources |  Alternative Data Sources | ICD Codes | Analysis Check List | Method of Calculation |  Basic Categories | Indicator Comments | Cross-References to Other Sections | References
  • The incidence rate is the total number of cases of selected sexually transmitted infections relative to the total population (per 100,000).
  • Age-specific incidence rates are the annual number of new cases of selected sexually transmitted infections in a given age group per 100,000 population in that age group.
  • Age-standardized incidence rate (SRATE): the number of new cases of selected sexually transmitted infections that would occur in the population if it had the same age distribution as the 1991 Canadian population.
  • Standardized incidence ratio (SIR): the ratio of observed new cases of selected sexually transmitted infections to the number expected if the population had the same age-specific incidence rates as Ontario.


Specific Indicators
  • Incidence of chlamydia
  • Incidence of gonorrhea
  • Incidence of syphilis (primary, secondary and congenital)
  • Incidence of HIV
  • Incidence of AIDS

Corresponding Mandatory Objectives

  • To reduce the incidence rate of gonorrhea to 15 per 100,000 population by the year 2005.
  • To reduce the incidence rate of genital chlamydia to 500 per 100,000 women ages 15-24 years by the year 2005.
  • To maintain the incidence rate of primary and secondary syphilis at less than one per 100,000 population by the year 2005.
  • To maintain the incidence of congenitally acquired syphilis at zero.
  • To reduce the number of newly diagnosed human immunodeficiency virus (HIV) infections to less than 800 per year by the year 2005.
  • To reduce the incidence of perinatal HIV infection.

Corresponding Outcomes from the Draft Ontario Public Health Standards (OPHS)

  • There are reduced transmission and incidence rates of sexually transmitted infections and blood-borne infections. (Societal)

Corresponding Health Indicator(s) from Statistics Canada and CIHI

  • None

Corresponding Indicators from Other Sources

Comparable health indicators: (Select "View" under latest issue then "Data tables") 

  • Incidence rate for chlamydia
  • Rate of newly reported HIV cases Integrated Public Health Information System, [Public Health Unit]

Data Sources

Numerator: Reportable Disease Data
Original source: Integrated Public Health Information System, [Public Health Unit]
Distributed by: Public Health Unit
Suggested citation (see Data Citation Notes): iPHIS [years], Extracted: [date]

Denominator: Population Estimates
Original source: Statistics Canada
Distributed by: Provincial Health Planning Database (PHPDB), Ontario MOHLTC
Suggested citation (see Data Citation Notes): Population Estimates [years]*, Provincial Health Planning Database (PHPDB) Extracted: [date], Ontario MOHLTC
* Note: Use the total years of the estimates, including the most recent year, even if not all were used in the analysis. The years used in the analysis should be included in the report itself.
Analysis Check List

  • Consider aggregation of data values and/or cell suppression when appropriate when dealing with small numbers to avoid risk of confidentiality breach. A new resource is currently under development to provide more detailed information on this issue.
  • For iPHIS: 
    • Ensure that the "diagnosing health unit" is the health unit of interest. 
    • To include only cases (and not case contacts or reports that were investigated and subsequently found not to be a case): Encounter Type = Case AND Diagnosis Status = Confirmed. For carriers, Encounter Type = Carrier AND Diagnosis Status = Carrier. 
    • Note that some diseases can occur more than once within the same person.

Method of Calculation

Total Incidence Rate:

total number of new cases of disease in a specified time period

    x 100,000

total population during the specified time period

Age-Specific Incidence Rates:

total number of new cases of disease in an age group in a specified time period

    x 100,000

total population in that age group in a specified time period

SRATE (See Resources: Direct Standardization (SRATES)):

Sum of (new cases of disease in a given age group * 1991 Canadian population in that age group)

    x 100,000

Sum of 1991 Canadian population

SMR (See Resources: Indirect Standardization (SMRs, SIRs)):

Sum of new cases of disease in the population 


Sum of (Ontario age-specific rate * population in that age group)

Basic Categories

  • Age groups for age-specific rates: 0-9, 10-14, 15-19, 20-24, 25-29, 30-34, 35-39, 40+, total
  • Sex: male, female
  • Geographic areas: Public Health Unit
  • Time period

Indicator Comments

  • Syphilis has several stages: congenital, primary, secondary and latent. The rate of congenital syphilis is one indicator while the rate of combined primary and secondary syphilis is a second indicator. Latent syphilis is not used in the calculation of rates since such persons are usually not infectious and represent previous infections.
  • Each health unit has its own database called the Integrated Public Health Information System (iPHIS) which is used to collect this data. Provincial summaries are compiled by the Ontario Ministry of Health and Long Term Care's Infectious Diseases Branch, which allows for comparisons with Ontario rates. Comparisons with other health units can be problematic however, because of inconsistencies across health units.1 Some cases may also be double-counted among people who move or cross various health unit boundaries.
  • iPHIS was implemented in every Ontario health unit in 2005.
  • There were some issues around data integrity when the previous reporting system, the Reportable Disease Information System (RDIS) was first implemented in 1990. For some diseases, case definitions have changed over time. These data quality issues remain relevant, as RDIS cases were migrated into iPHIS. See Resources: Canadian and Ontario Case Definitions for Infectious Diseases.
  • There may be considerable under-reporting of actual cases for some diseases in iPHIS. For instance, when an infected person has mild clinical symptoms they may not seek medical care and/or laboratory testing may not be performed.
  • To best understand mortality or disease trends in a population, it is important to determine crude rates, age-specific rates and age-standardized rates (SRATES) or ratios (SMRs, SIRs). The crude death (or disease) rate is the number of deaths (or disease cases) divided by the number of people in the population. This rate depicts the “true” picture of death /disease in a community although it is greatly influenced by the age structure of the population. An older population would likely have a higher crude death rate whereas a younger population may have a higher crude birth rate. Age-specific rates can best describe the “true” death /disease pattern of a community and allow comparison of populations that have different age structures.
  • Since many age-specific rates are cumbersome to present, age standardized rates have the advantage of providing a single summary number that allows different populations to be compared; however, they present an “artificial” picture of the death /disease pattern in a community. It is important to examine the data carefully before standardizing. In general, the SMR or SIR is used to compare an area (e.g., health unit) with one other area (e.g., Ontario). This indirect form of standardization requires a comparator that has a large population and stable age-specific rates. SRATEs, on the other hand, are generally used to compare a number of rates at the same time, e.g., health units across a region or rates over time. This direct form of standardization requires all comparators to have relatively stable age-specific rates. For more information about standardization, refer to the Resources section: Direct Standardization (SRATES) and Indirect Standardization (SMRs, SIRs).

Cross-References to Other Sections

Cited References

  1. Dawson K. Data Quality in RDIS: Issues related to Combining Data Sets. Central East Health Information Partnership, October 2000. 

Other References

  • Evans AS, Brachman PS. Bacterial Infections in Humans: Epidemiology and Control. Springer, 1998.
  • Heymann DL. Control of Communicable Diseases Manual. American Public Health Association, 2004.
  • Alexander D. Epidemiology of AIDS/TB coinfection in Ontario – 1990-1995. PHERO, Volume 8(4), April 25, 1997;94-98.
  • Public Health Agency of Canada. 2004 Canadian Sexually Transmitted Infections Surveillance Report. CCDR 2007;33S1:1-69. Available at:

Changes to Indicator June 2008

  • Changed all references of Sexually Transmitted Disease to Sexually Transmitted Infection
  • Added related outcomes from draft Ontario Public Health Standards
  • Removed suggestion to suppress cell counts less than five and added comment on confidentiality issues
  • Updated indicator comments, especially to reflect change of source from RDIS to iPHIS
  • Updated references

Date of Last Revision: June 13, 2008.

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