DPH: Technical notes about methods

Technical notes about methods


HIV Statistics

HIV Surveillance Program Home Page


Uses of HIV surveillance information – The primary goal of the HIV Surveillance Program is to systematically collect, analyze, interpret, and disseminate information about trends in cases of HIV infection in Connecticut. This information is used by a variety of state and federal agencies to develop policy and allocate funding for local prevention and care needs. Media such as television and newspapers use surveillance data to describe HIV in Connecticut. Local health departments, non-government organizations and agencies, hospitals, physicians, students and others also use HIV surveillance data. Other important functions of the surveillance system at the state and national level include identification of clusters, unusual cases of transmission, emerging genetic variants, and drug-resistant strains.

Reportable diseases – Connecticut laws require the Department of Public Health to maintain a list of reportable diseases. The list includes approximately 60 diseases and conditions of public health importance. To be reported, a person with the disease or condition must meet the surveillance “case definition.” Cases are reported by the diagnosing physician and the laboratory that performs the test.

HIV infection surveillance – HIV infection is a reportable condition. The HIV case definition consists of laboratory evidence of HIV infection using a combination screening test and other confirmatory test such as PCR. The AIDS case definition consists of either HIV positive with a low CD4-positive cell count (below 200 cells/microliter or less than 14% of total lymphocytes), or HIV positive and a diagnosis with one of several opportunistic infections or conditions (for example, Pneumocystis jirovecii pneumonia or cervical carcinoma). HIV cases are re-reported if they meet the AIDS case definition. However, a person with HIV infection is only counted once, as an HIV infection case. The Department of Public Health maintains a computerized registry of HIV infection cases.

How are HIV infection cases counted? - Trends in HIV cases are typically provided using year of diagnosis although trends in year of report have been used in the past and can still be used if the need arises. Data is displayed using residence at diagnosis unless otherwise noted.
• Year of report of HIV infection – This is the year in which a person with HIV infection is reported with a diagnosis of HIV infection regardless of HIV or AIDS status. This data gives a trend in new reports of HIV infection.

• Year of diagnosis with HIV infection – This is the year in which the case was diagnosed with HIV infection regardless of HIV or AIDS status and irrespective of the year of report. For example, a case could be reported in 2008 that represents a person diagnosed in 2008, 2007, or earlier. This data is affected by the lag in reporting (interval between diagnosis and report to DPH) and more recent years will be undercounted. The year of diagnosis is established by the earliest confirmatory HIV test or earliest diagnosis date documented in the medical record. Tables with this data will not include the current year.


Information collected about HIV infection cases – Various demographic and medical information is collected about each case of HIV/AIDS including: laboratory test dates, sex, race, town of residence, exposure category, AIDS indicator diseases, treatment status, pregnancy status, and provider information. Additional information about some of these data elements is shown below.

• Year of report – The year of report is based on the date that the case was first reported to the Department of Public Health. Reporting delay results in an undercount of recently diagnosed cases.

• Sex – For each case of HIV infection, information is collected about the person’s sex at birth: male, female, or unknown. Other gender identities can be reported and are collected as current gender.

• Race/Ethnicity – For each case of HIV infection, information is collected about the person’s race and ethnicity. The following are race categories:  White, Black, Asian, Native Hawaiian or other Pacific Islander, and American Indian/Alaska Native. Ethnicity is coded separately as Hispanic or Not Hispanic. Cases can be reported with more than one race.

• City of residence – The city of residence refers to the city where the person resided at the time of their initial diagnosis of HIV and or AIDS.

• Vital status – Annually, the HIV surveillance registry is matched with the vital records death registry to update the vital status for each case.  Persons living with HIV are cases for which death has not been reported. There is a lag in the reporting of deaths so the most recent two to three years are under counts.

• Exposure categories – For each case of HIV infection, information is collected about the most likely source of HIV infection. This information is referred to as the exposure category, mode of transmission, risk group, or risk factor. This information may not always be available, especially for recently reported cases. The provider may not have reported the information, or the patient may not have volunteered the information, may not be in care, or may have died. When the exposure category is unknown, the Department of Public Health HIV tables and graphs classify these cases in a separate category, “Other/Unknown.” Over time, after additional follow-up with providers, many of these cases will be reclassified into one of the exposure categories. In the HIV Surveillance System, HIV cases are only counted once in a hierarchy of exposure categories. Persons with more than one category are classified in the exposure category listed first in the hierarchy, except for men with both a history of sexual contact with other men and injection drug use. These men are in a separate category. All exposures refer to experiences of the case that took place after 1977 and before their first positive HIV test.

Men who have sex with men (MSM) – Men who report having sexual contact with men (homosexual contact) and men who report sexual contact with both men and women (bisexual contact).

Injection drug use (IDU) – Persons who have injected non-prescription drugs.

Heterosexual contact – Persons who have had heterosexual sex with a person with HIV infection or who is at high risk of HIV infection.

o Presumed Heterosexual contact - A female (based on birth sex) with a history of sexual contact with a male, and not classified as an IDU or with any other risk factor.

o Perinatal - The child's mother has or had (if deceased) HIV infection (mother-to-child exposure).

Other – Other exposure categories include received clotting factor for hemophilia/coagulation disorder, transfusion recipient, transplant recipient, and worker in a health care setting. Due to low numbers, these cases are classified together as “Other” in HIV tables and graphs.

• Opportunistic infections – There are 26 opportunistic infections or conditions that, together with HIV infection, indicate development of AIDS. These are also referred to as “AIDS indicator diseases.” Many of these diseases result from impaired immunity. Having one of these diseases does not necessarily indicate that the person has HIV infection. The HIV surveillance system collects information on the disease(s) that are reported with the initial diagnosis of HIV. Indicator diseases that are subsequently diagnosed are not systematically monitored.

HIV in children – Information specific for pediatric cases of HIV (<13 years of age) are also collected. A pediatric case report form is used to collect this information. In addition to routine surveillance, the Department of Public Health has been conducting an enhanced surveillance project for perinatal exposure to HIV since 1999. For each case of perinatal HIV exposure, an extensive medical record extraction is conducted for the mother-child pair. Information collected about the mother includes demographics, risk behavior, HIV testing information, compliance with prenatal care, and types and duration of HIV treatment during pregnancy and labor/delivery. Information collected about the infant includes HIV preventive treatment, testing information, final HIV status, and birth defects.

Incidence – Incidence rate is defined as the number of new cases in a defined population within a specified time period. To calculate incidence, the number of new cases of the disease and the size of the population at risk are needed. In the following example, the 2002 incidence of AIDS is calculated for Stamford and New London.  Note, that in this example, the smaller city with a fewer number of cases has a higher incidence rate.

• Stamford: [26 (AIDS cases) divided by 117,083 (population)] multiplied by 100,000 equals 22 per 100,000
• New London: [12 (AIDS cases) divided by 25,671 (population)] multiplied by 100,000 equals 46 per 100,000
• Incidence rates can be calculated for any group for which both the number of new cases and the size of the population are known. For example, rates can be calculated for gender, race, and age groups. Generally, population data is taken from the US Census, conducted every ten years, most recently in 2010 (see www.census.gov).
• Incidence rates cannot be calculated for some subgroups (i.e., IDU, MSM) because the size of these populations is unknown. Rates in populations of small size, such as small towns, can be misleading because the presence of a single case or few cases within a small population can make a rate appear large.

Prevalence – Prevalence is the number of existing cases of a disease in a defined population at a point in time. The prevalence of people living with HIV (PLWH) for Stamford and New London on December 31, 2002 is shown below.

• Stamford: [356 (PLWA) divided by 117,083 (population)] multiplied by 100,000 equals 304 per 100,000
• New London: [138 (PLWA) divided by 25,671 (population)] multiplied by 100,000 equals 537 per 100,000

Centers for Disease Control and Prevention (CDC) – CDC funds most HIV surveillance activities throughout the United States. CDC provides the case report form and computerized registry used by the surveillance system in each state. The Department of Public Health reports HIV data to CDC on a monthly basis. The information provided to CDC does not include personal identifiable data. CDC uses information from all states to compile national statistics about HIV.

Confidentiality of personal information – Surveillance data include information about persons with reportable diseases including name, address, and other personal information. Connecticut law prohibits release of this information to unauthorized persons. Only authorized persons within the Department of Public Health have access to this information. Only de-identified information is reported to CDC. Information is analyzed and disseminated in aggregate only.

Content Last Modified on 2/2/2017 8:54:42 AM