All 50 states, the District of Columbia, U.S. dependencies and possessions, and independent nations in free association with the United States¹ report AIDS cases to CDC using a uniform surveillance case definition and case report form. The original definition was modified in 1985 (MMWR 1985;34:373-75) and 1987 (MMWR 1987;36[suppl. no. 1S]:1S-15S). The case definition for adults and adolescents was modified again in 1993 (MMWR 1992;41[no. RR-17]:1-19; see also MMWR 1995;44:64-67). The revisions incorporated a broader range of AIDS-indicator diseases and conditions and used HIV diagnostic tests to improve the sensitivity and specificity of the definition. The laboratory and diagnostic criteria for the 1987 pediatric case definition (MMWR 1987;36:225-30, 235 ) were updated in 1994 (MMWR 1994;43[no. RR-12]:1-19). Effective January 1, 2000, the surveillance case definition for HIV infection was revised to reflect advances in laboratory HIV virologic tests. The definition incorporates the reporting criteria for HIV infection and AIDS into a single case definition for adults and children (MMWR 1999;48[no.RR-13]:29-31).

The pediatric case definition incorporates the revised 1994 pediatric classification system for evidence of HIV infection. Cases among children with their first positive results on Western blot or HIV detection tests before October 1994 were categorized based on the 1987 classification system. Cases among those tested during or after October 1994 are categorized under the revised 1994 pediatric classification system. For children of any age with an AIDS-defining condition that requires evidence of HIV infection, a single positive HIV virologic test (i.e., HIV nucleic acid [DNA or RNA], HIV viral culture, HIV p24 antigen) is sufficient for a reportable AIDS diagnosis if the diagnosis is documented by a physician.

Although completeness of reporting of diagnosed AIDS cases to state and local health departments varies by geographic region and patient population, studies conducted by state and local health departments indicate that reporting of AIDS cases in most areas of the United States is more than 85% complete (J Acquir Immune Def Syndr 1992;5:257-64, Am J Public Health 1992;82:1495-99, AIDS 1999; 13:1109-14, and Ann Epidemiol 2001;11:443-449.). In addition, multiple routes of exposure, opportunistic diseases diagnosed after the initial AIDS case report was submitted to CDC, and vital status may not be determined or reported for all cases. However, among persons reported with AIDS, reporting of deaths is estimated to be more than 90% complete (JAMA 1996;276:126-31). CDC estimates approximately 3% of AIDS cases are duplicates based on matching within the national coded surveillance database.

Since January 1, 1994, CDC has not accepted AIDS case reports that meet only the laboratory-based immunologic criteria of the 1993 expanded surveillance case definition (MMWR 1991;41[no. RR-17]:1-19) if they were missing information on sex or race/ethnicity. A small number of cases previously reported to CDC that were missing those variables have been returned to the health departments for follow-up and have been deleted from the totals. Included in this report are persons known to be infected with human immunodeficiency virus type 2 (HIV-2). See MMWR 1995;44:603-06.

Surveillance of HIV infection

This report includes HIV case reports from 39 areas that had laws or regulations requiring confidential reporting by name of adults/adolescents, and children with confirmed HIV infection, in addition to reporting of persons with AIDS, through December 31, 2001. Connecticut required reporting by name of HIV infection only for children <13 years of age; and Oregon required reporting only for children <6 years of age until October 2001. After removal of personally identifying information, these reports were submitted to CDC, and are included in this report (see table 3 for listing). States have initiated HIV reporting at various times after the development of serum HIV-antibody tests. Before 1991, surveillance of HIV infection was not standardized and reporting of HIV infections was based primarily on passive surveillance. Many cases reported before 1991 do not have complete information. Since then, CDC has assisted states in conducting active surveillance of HIV infections using standardized report forms and software. However, collection of demographic and risk information still varies among states.

HIV infection data should be interpreted with caution. HIV surveillance reports may not be representative of all persons infected with HIV since not all infected persons have been tested. Many HIV-reporting states offer anonymous HIV testing and home collection HIV test kits are widely available in the United States. Anonymous test results are not reported to state and local health departments’ confidential name-based HIV registries. Therefore, confidential HIV infection reports may not represent all persons who tested positive for HIV infection. Furthermore, many factors may influence testing patterns, including the extent that testing is targeted or routinely offered to specific groups and the availability of and access to medical care and testing services. These data provide a minimum estimate of the number of persons known to be HIV infected in states with confidential HIV reporting.

As of December 31, 2001, 9 areas (DC, HI, IL, KY, MD, MA, PR, RI, and VT) had implemented a code-based system to conduct case surveillance for HIV infection. Some other areas (DE, ME, MT, OR, and WA) had implemented a name-to-code system to conduct HIV infection surveillance: initially, names are collected and, after any necessary public health follow-up, names are converted to codes. Data on cases of HIV infection from these areas are not included in the HIV data tables pending evaluations demonstrating acceptable performance under CDC guidelines and the development of methods to report such data to CDC.

For this report, cases among adults, adolescents, and children ≥18 months of age, were classified using the 2000 revised HIV surveillance case definition which incorporates positive results or reports of a detectable quantity of HIV nucleic acid or plasma HIV RNA (MMWR 1999;48[no. RR-13]:29-31). For children <18 months of age, the pediatric HIV reporting criteria reflect diagnostic advances that permit the diagnosis of HIV infection during the first months of life. With HIV nucleic acid detection tests, HIV infection can be detected in nearly all infants aged one month and older. The timing of the HIV serologic and HIV nucleic acid detection tests and the number of HIV nucleic acid detection tests in the definitive and presumptive criteria for HIV infection are based on the recommended practices for diagnosing infection in children aged <18 months and on evaluations of the performance of these tests for children in this age group. Children aged <18 months born to an HIV-infected mother will be categorized as having perinatal exposure to HIV infection if the child does not meet the criteria for HIV infection or the criteria for “not infected with HIV” (MMWR 1999;48[no. RR-13]:29-31) MMWR 1998;47 [no. RR-4]). Children born before 1994 were considered HIV-infected if they met the HIV case definition stated in the 1987 pediatric classification system for HIV infection (MMWR 1987;36: 225-30,235).

Because states initiated reporting on different dates, the length of time reporting has been in place will influence the number of HIV infection cases reported. For example, data presented for a given annual period may include cases reported only during a portion of the year. Prior to statewide HIV reporting, some states collected reports of HIV infection in selected populations. Therefore, these states have reports prior to initiation of statewide confidential reporting. A state with confidential HIV infection reporting also may report persons who tested positive in that state but who were residents of other states. Therefore, when HIV data are presented by state of residence, cases reported prior to the date a state initiated reporting may have been reported from other states with confidential HIV infection reporting.

Over time, persons with HIV infection may develop AIDS and be reported to surveillance. HIV infection cases later reported with AIDS are deleted from the HIV infection tables and added to the AIDS tables. Persons with HIV infection may be tested at any point in the clinical spectrum of disease; therefore, the time between diagnosis of HIV infection and AIDS will vary. In addition, because surveillance practices differ, reporting and updating of clinical and vital status of cases vary among states. Completeness of reporting for HIV is estimated to be more than 85% complete (MMWR 1998;47:309-14). CDC estimates approximately 2% of HIV cases are duplicates based on matching within the national coded surveillance database.

Tabulation and presentation of data

Data in this report are provisional. Each issue of this report includes information received by CDC through the last day of the reporting period. In the first part of the report (through table 21), HIV and AIDS data are tabulated by date of report to CDC. In the second part of the report (from table 22 through table 33), data are statistically adjusted to correct for temporal delays in the reporting of cases and deaths, and unreported risk/exposure is statistically redistributed in order to improve the presentation of trends in the epidemic and the distribution of risk characteristics among affected populations. Data for U.S. dependencies and possessions and for associated independent nations are included in the totals.

Age group tabulations for table 1 are based on the person’s calculated age as of December 31, 2001. All other age group tabulations are based on the person’s age at first documented positive HIV-antibody test for HIV infection cases, and age at diagnosis of AIDS for AIDS cases. Adult/adolescent cases include persons 13 years of age and older; pediatric cases include children under 13 years of age.

Tabulations of persons living with HIV infection and AIDS (table 1) include persons whose vital status was reported “alive” as of last update; persons whose vital status is missing or unknown are not included. Tabulations of deaths in persons with AIDS include persons whose vital status was reported “dead” as of last update; persons whose vital status is missing or unknown are not included. Caution should be used in interpreting these data because states vary in the frequency with which they review the vital status of persons reported with HIV infection and AIDS. In addition, some cases may be lost to follow-up.

Table 4 lists AIDS case counts for each metropolitan area with a census 2000 population of 499,999 or more. AIDS case counts for metropolitan areas with 50,000 to 499,999 population are reported as a combined subtotal. On December 31, 1992, the Office of Management and Budget announced new Metropolitan Statistical Area (MSA) definitions, which reflect changes in the U.S. population as determined by the 1990 census. These definitions were updated most recently on June 30, 1998. The cities and counties which compose each metropolitan area listed in table 4 are provided in the publication “Metropolitan Areas as of June 30, 1998” (available by calling the National Technical Information Service, 1-703-487-4650, and ordering accession no. PB98-502198 or by visiting http://www.census.gov/population/www/estimates/metrodef.html). Standards for defining central and outlying counties of metropolitan areas were published in the Federal Register (FR 1990;55:12154-60).

The metropolitan area definitions are the MSAs for all areas except the 6 New England states. For these states, the New England County Metropolitan Areas (NECMA) are used. Metropolitan areas are named for a central city in the MSA or NECMA, may include several cities or counties, and may cross state boundaries. For example, AIDS cases and annual rates presented for the District of Columbia in table 2 include only persons residing within the geographic boundaries of the District. AIDS cases and annual rates for Washington, D.C., in table 4, include persons residing within the several counties in the metropolitan area, including counties in Maryland, Virginia, and West Virginia. State or metropolitan area data tabulations are based on the person’s residence at first positive HIV-antibody test result for HIV infection cases, and residence at diagnosis for the first AIDS indicator condition(s) for AIDS cases.

Regions of residence included in this report are defined as follows. Northeast: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont; Midwest: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin; South: Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia; West: Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming; Territories: Guam, Puerto Rico, the U.S. Pacific Islands listed in the footnote on the first page of these notes, and the U.S. Virgin Islands.

Estimated AIDS incidence (tables 22, 23, and 24), estimated AIDS incidence trends (tables 25, 26, and 27 and figure 6), estimated number of persons living with AIDS (tables 28, 29, and 30), and estimated number of deaths (tables 31, 32, and 33) are not actual counts of cases reported to the surveillance system. The estimates are based on reported cases which have been adjusted for delays in reporting of cases and deaths and a number of assumptions. The date of death for decedents with a missing date of death was imputed as the date that death was reported to CDC minus the estimated median months required to report deaths. For these estimates, the median reporting delay for deaths was 3 months. If AIDS diagnosis occurred after the date imputed, then the date of AIDS diagnosis was used as the date of death. While these tables were constructed using the best methods currently available, there is inherent uncertainty in these estimates (Lecture Notes in Biomathematics 1989; 83:58-88). Small numbers must be interpreted with caution because the inherent uncertainty in estimates is greater for small numbers.

Exposure categories

For surveillance purposes, HIV infection cases and AIDS cases are counted only once in a hierarchy of exposure categories. Persons with more than one reported mode of exposure to HIV 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 injecting drug use. They make up a separate exposure category.

“Men who have sex with men” cases include men who report sexual contact with other men (i.e., homosexual contact) and men who report sexual contact with both men and women (i.e., bisexual contact). “Heterosexual contact” cases are in persons who report specific heterosexual contact with a person with, or at increased risk for, HIV infection (e.g., an injecting drug user).

Adults/adolescents born, or who had sex with someone born, in a country where heterosexual transmission was believed to be the predominant mode of HIV transmission (formerly classified as Pattern-II countries by the World Health Organization) are no longer classified as having heterosexually-acquired AIDS unless they meet the above stated criteria. Similar to other cases among persons who were reported without behavioral or transfusion risks for HIV, these cases are now classified (in the absence of other risk information which would classify them in another exposure category) as “no risk reported or identified” (MMWR 1994;43:155-60). Cases among children whose mother was born, or whose mother had sex with someone born, in a Pattern II country are now classified (in the absence of other risk information which would classify them into another exposure category) as “Mother with/at risk for HIV infection: has HIV infection, risk not specified.”

Cases among persons with no reported history of exposure to HIV through any of the routes listed in the hierarchy of exposure categories are classified as “no risk reported or identified.” NIR cases include those which are currently being followed up by local health department officials; cases among persons whose exposure history is incomplete because they died, declined to be interviewed, or were lost to follow up; and cases among persons who were interviewed or for whom other follow-up information was available and no exposure mode was identified. Cases among persons who have an exposure mode identified at the time of follow-up are reclassified into the appropriate exposure category. Historically, investigations and follow-up for modes of exposure by state health departments were conducted routinely for persons reported with AIDS and as resources allowed for persons reported with HIV infection. Therefore, the percentage of cases among HIV infected persons with risk not reported or identified is substantially higher than for those reported with AIDS.

As of September 2000, the procedures for the investigation of cases reported without risk changed from ascertaining risk for all reported cases to estimating risk distributions from statistical models and population-based samples. States continue to investigate any report of an unusual exposure to HIV and report these cases to CDC. CDC will continue to tabulate the number of documented unusual exposures to HIV as reported by the states.

Because recently reported AIDS cases are more likely to be reported as NIR, recent AIDS incidence in some exposure categories will be underestimated unless an adjustment is made. For estimated AIDS incidence tables and estimated AIDS trends figures, the adjustment of NIR adult/adolescent cases is based on sex-, race-, and region-specific exposure category redistributions of cases diagnosed from 1990 through 1998 that were initially assigned to the NIR category but have subsequently been reclassified. Similar adjustment of NIR pediatric cases are based on exposure category redistribution of all cases diagnosed between 1990 through 1998 and subsequently reclassified. See J Acquir Immune Def Syndr, 1992;5:547-55 and J Acquir Immune Def Syndr, 1997;14:465-74.

Trends in AIDS incidence

Because of the temporary distortion caused by the 1993 expansion of the case definition, trends in AIDS incidence had previously been estimated by statistically adjusting cases reported based on the criteria added to the case definition in 1993. This adjustment estimated when persons reported on the basis of immunologic criteria (CD4+ T-lymphocytes counts less than 200 cells/µL or percentage less than 14) would develop an AIDS-related opportunistic illness (AIDSOI), and thereby approximated trends in AIDS-OI incidence as if the case definition had not changed (J Acquir Immune Defic Syndr 1997;16:116-21). However, by the end of 1996, the temporary distortion caused by reporting prevalent as well as incident cases that met criteria added in 1993 had almost entirely waned. In addition, after the end of 1996, the incidence of AIDS-OIs could no longer be reliably estimated because data are not currently available to model the increasing effects of therapy on rate of disease progression. Therefore, from 1996 forward, trends in AIDS incidence are adjusted for reporting delay, but not for the 1993 expansion of the case definition. These trends represent the incidence of AIDS (1993 criteria) in the population and increasingly represent persons with HIV newly diagnosed at the time of AIDS diagnosis, those identified with HIV who did not seek or receive treatment, and those for whom treatment has failed. Thus, despite the effects of treatment on AIDS incidence, AIDS incidence remains an important measure of the impact and need for resources for the severely ill.

Reporting delays

Reporting delays (time between diagnosis of HIV infection or AIDS and report to CDC) may vary among exposure, geographic, racial/ethnic, age, sex, and vital status categories, and have been as long as several years for some AIDS cases. About 52% of all AIDS cases were reported to CDC within 3 months of diagnosis and about 88% were reported within 1 year. Among persons with AIDS, estimates of death reporting delay show that approximately 88% of deaths are reported within 1 year. For HIV infection cases diagnosed since implementation of uniform reporting through the HIV/AIDS reporting system on January 1, 1994, about 66% of all HIV infection cases were reported to CDC within 3 months of diagnosis and about 93% were reported within 1 year.

Reporting delay adjustments to estimated AIDS data are calculated by a maximum likelihood statistical procedure, taking into account differences in reporting delays among exposure, geographic, racial/ ethnic, age, sex, and vital status categories, and assuming that reporting delays within these groups have not changed over time (Statist Med 1998;17:143-54 and Lecture Notes in Biomathematics 1989;83:58- 88).

Rates

Rates per 100,000 population were calculated for AIDS cases. Population denominators for computing AIDS rates for the 50 states and the District of Columbia were based on official postcensus estimates and census 2000 counts from the U.S. Bureau of Census. Denominators for U.S. dependencies and possessions and associated independent nations were based on official postcensus estimates from the U.S. Bureau of the Census International Database. Each 12-month rate is calculated by dividing the number of cases reported during the 12-month period by the 2000 or 2001 population, multiplied by 100,000. The denominators used for computing the table of race-specific rates (year-end edition only) are based on the 2001 census estimates published by the U.S. Bureau of Census (http://www.census.gov/). The age/sex/race proportions from the 2000 census were applied to the census 2001 national population total to estimate the age, sex, and race-specific subpopulations. Race-specific rates are calculated by dividing the number of cases reported for a particular racial/ethnic group during the preceding 12- month period by the projected population for that race/ ethnicity, multiplied by 100,000.

¹Included among the dependencies, possessions, and independent nations are Puerto Rico, the U.S. Virgin Islands, Guam, American Samoa, the Republic of Palau, the Republic of the Marshall Islands, the Commonwealth of the Northern Mariana Islands, and the Federated States of Micronesia. The latter 5 comprise the category “Pacific Islands, U.S.” listed in tables 1 and 2.