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Evaluation of HIV Case Surveillance Through the Use of Non-Name Unique Identifiers -- Maryland and Texas, 1994-1996

Notifiable disease reporting laws or regulations in states and territories require reporting of acquired immunodeficiency syndrome (AIDS) cases, including patient and physician names, to state or local health authorities. As of January 1, 1998, a total of 31 states were conducting name-based human immunodeficiency virus (HIV) case surveillance by using the same methods as surveillance for AIDS. However, because of concerns about name-based HIV surveillance, Maryland and Texas implemented HIV surveillance using non-name unique identifiers (UI)*. This report summarizes a 3-year collaboration by CDC and these states to evaluate UI surveillance for HIV infection; the findings indicate some limitations to the use of a Social Security number-based UI for HIV surveillance.

In both Maryland and Texas, UI surveillance for HIV was implemented in early 1994, and both used the same 12-digit numeric UI code (comprising the last four digits of the patient's Social Security number {SSN}, six-digit {month/day/year} date of birth {DOB}, one-digit code for race/ethnicity, and one-digit code for sex). HIV-infection reports included residence data, diagnosing facility, and date of test, but did not include mode of HIV exposure. In both states, UI HIV surveillance databases were maintained separately from name-based AIDS surveillance databases.

Evaluation criteria included the proportion of reports with full UI codes, timeliness and completeness of HIV reporting, and potential for matching the UI-based case reports to alternate databases. In Texas, selected HIV reports also were evaluated for ability to follow back UI reports to patient records; in Maryland, provider compliance with maintaining patient surveillance logs was assessed. During July 1994-December 1996, Maryland reported 6412 AIDS cases and received 9971 HIV-infection reports, and Texas reported 12,041 AIDS cases and received approximately 23,000 HIV-infection reports. Maryland

In 1993, the Maryland legislature mandated UI reporting of both positive HIV tests and patients with CD4+ T-lymphocyte counts of less than 200 cells/uL (CD4+)**. Health-care providers requesting HIV or CD4+ tests are required to construct the UI code for each patient, include the code on the laboratory slip, and record it in a surveillance log that matches the UI to patient identifiers (e.g., medical record number, patient name, or other patient code) for purposes of case investigation and follow up. Laboratories licensed by Maryland are required to submit the UI-based reports to the state health department through the local health departments.

Of 9971 HIV-infection reports entered during July 1994-December 1996, all UI elements were present for 7119 (71%) (Table_1). Element-specific presence ranged from 78% (SSN) to 98% (DOB and sex). The proportion of reports with full UI increased during July 1994-June 1996, and declined slightly during July-December 1996. The median time from date of HIV test to receipt of report by the state health department was 20 days (range: 1-847 days). During October-November 1997, all 72 providers in nine counties of eastern Maryland (the counties reported 3% of AIDS cases in Maryland in 1996) for whom laboratories had submitted HIV-infection reports were contacted to determine the proportion of providers who maintain the required surveillance log linking UI to patient identifiers; 32 (44%) of these providers maintained logs.

Completeness of HIV-infection reporting was estimated by comparison to cases of AIDS reported in the AIDS surveillance registry. Of AIDS cases with dates of HIV diagnosis from July 1995 through June 1996, data elements to construct UI were available for 633 (85%) cases. Of these, 319 (50%) matched to HIV-infection reports with full UI in the UI database (Table_2).

Data from the Maryland HIV counseling and testing (C&T) system (excluding sites offering only anonymous HIV tests) were used to evaluate the proportion of records with full UI and completeness of HIV-infection reporting. In early 1995, counselors were instructed to obtain UI code information from clients and record the UI on the HIV C&T record. During 1995-1996, a total of 1093 records with a positive HIV test were entered into the C&T database; of these, all UI elements were present for 94%. HIV C&T reports for persons who had HIV diagnosed from July 1995 through June 1996 were matched to the UI database. Of the 528 reports, 276 (52%) matched. Texas

In 1994, the Texas Board of Health amended regulations to require named reporting of HIV-infected children aged less than 13 years and UI reporting of HIV-infected adolescents and adults. Both health-care providers ordering an HIV test and laboratories performing the test report confirmed HIV infections to the Texas Department of Health (TDH) through the local health departments. Neither providers nor laboratories are required to maintain registries linking UI to patient identifiers.

Approximately 23,000 HIV-infection reports were received at TDH during the evaluation period. Since 1995, TDH excluded approximately 7000 paper HIV reports with three or more missing UI data elements. Of 16,119 HIV-infection reports entered into the UI database, all UI elements were present for 9923 (62%) (Table_1). Element-specific presence ranged from 66% (SSN) to 97% (sex). Overall, 60% of reports were submitted in periodic batches, which had a longer time from date of HIV test to receipt by TDH (median: 173 days; range: 26-974 days) than the 40% of reports submitted individually (median: 59 days; range: 2-906 days).

Completeness of HIV-infection reporting was estimated by comparison to AIDS surveillance data using the same methodology as in Maryland. Data elements to construct UI were available for 1762 (79%) of AIDS cases with dates of HIV diagnosis in the specified period (Table_2). Of these, 454 (26%) matched to HIV-infection reports with full UI in the UI database.

To evaluate the feasibility of epidemiologic follow up, TDH sampled 765 HIV-infection reports submitted during January 1995-June 1996, in six areas of the state, reflective of variation in geography, demography, HIV morbidity, and reporting sources. Of these, 456 (60%) could be matched to a client record using any combination of UI (including records without full UI), health-care provider name, date of test, residential information, and other locally available information. Matched records that were missing the SSN data element (n=208) were reviewed to determine whether these data could be located. SSN could not be located for 120 (58%) of these records.

Reported by: L Solomon, DrPH, L Eldred, DrPH, J Markowitz, PhD, P Ryan, MS, G Benjamin, MD, Maryland Dept of Health and Mental Hygiene. AS Robbins, PhD, DW Hamaker, SA King, MA, SK Melville, MD, MC Thomas, MS, DM Simpson, MD, State Epidemiologist, Texas Dept of Health. Div of HIV/AIDS Prevention-Surveillance and Epidemiology, National Center for HIV, STD, and TB Prevention, CDC.

Editorial Note

Editorial Note: HIV and AIDS surveillance data are needed to provide reliable population-based data to guide public health programs. During 1995-1996, the first declines in the incidence of AIDS-opportunistic infections and AIDS deaths were reported in the United States (6% and 23%, respectively), in part, as a result of increasingly effective HIV therapy (1). On the basis of revised HIV treatment guidelines (2), the impact of treatment advances on AIDS trends is expected to continue and will reduce the usefulness of AIDS data alone to monitor HIV-infection trends and morbidity. CDC and other public health and advocacy organizations have recognized the need for national HIV case surveillance while continuing to discuss the relative merits of HIV surveillance methods based on numeric codes compared to the name-based approach employed for AIDS surveillance (1,3).

CDC uses established criteria to evaluate performance of public health surveillance systems to provide accurate data to target prevention and care programs (4). States conduct active surveillance using existing name-based clinical and public health records to decrease the reporting burden on providers, eliminate duplicate reports, and facilitate epidemiologic follow-up. These methods enable AIDS surveillance to attain high performance standards as reflected by completeness of reporting ( greater than 85%) (5) and documentation of risk exposures ( greater than or equal to 93% of cases) (6). Evaluation of name-based HIV surveillance has shown 74%-97% completeness of reporting (7; CDC, unpublished data, 1997), and documentation of risk exposures ( greater than or equal to 76% of cases) (6). Secure and confidential surveillance practices are required as a condition for receipt of federal resources for HIV and AIDS surveillance. At the state level, the most comprehensive protections of medical data apply to government-held data, and most specifically to HIV-related data (8). Names are removed before encoded and encrypted AIDS or HIV surveillance data are transmitted to CDC.

The evaluations in Maryland and Texas indicated that the use of UIs limits the performance of an HIV surveillance system and complicates efforts to collect risk-behavior information. Both systems demonstrated timely reporting. Although data from both states indicated increases in reporting of the SSN data element during the evaluation period, overall 22% of reports in Maryland and 34% in Texas were missing the SSN element, which contributed to a high rate of incomplete case reporting. The follow-back investigation in Texas suggests that SSNs are not readily available in client or medical records but, in the controlled environment of the Maryland HIV C&T system, counselors were able to collect SSNs for most clients. The completeness of reporting also may be affected by the ability of providers and laboratories to use UIs as part of routine HIV-testing practices. For example, one large laboratory providing HIV-testing services in Maryland did not report HIV infections during the evaluation period. The difficulty in collecting HIV data when persons are tested out of state also may affect completeness of reporting and the ability to eliminate duplicate reports. Maryland is continuing to evaluate its UI surveillance system, and Texas is exploring alternative HIV surveillance systems with input from community groups.

Effective HIV surveillance systems must include HIV risk information; however, this information often is not available at the time of the initial UI case report, and follow-up with health-care providers is necessary. To supply follow-up information, health-care providers must use lists or other mechanisms to link the UI to patient identifiers. The UI approach complicates efforts to collect this information and increases the number of lists of HIV-infected persons that could be disclosed in a breach of confidentiality.

CDC has recommended that all states and territories conduct HIV case surveillance as an extension of their AIDS surveillance systems (1). In addition, CDC is developing technical guidance to enhance security practices, standardize confidentiality laws and regulations, and promote uniform standards for HIV case surveillance systems. These guidelines will assist states and territories in implementing HIV case surveillance using data-collection and data-storage methods that provide high quality HIV surveillance data while assuring the confidentiality of surveillance information.


  1. CDC. Update: trends in AIDS incidence, 1996. MMWR 1997;46:861-7.

  2. Carpenter CC, Fischl MA, Hammer SM, et al. Antiretroviral therapy for HIV infection in 1997: updated recommendations of the International AIDS Society-USA panel. JAMA 1997;277:1962-9.

  3. Council of State and Territorial Epidemiologists. CSTE: position statement ID-4. National HIV surveillance: addition to the National Public Health Surveillance System. Atlanta, Georgia: Council of State and Territorial Epidemiologists, 1997.

  4. Klaucke DN. Evaluating public health surveillance. In: Teutsch SM, Churchill RE, eds. Principals and practices of public health surveillance. New York, New York: Oxford University Press, 1994:158-74.

  5. Rosenblum L, Buehler JW, Morgan ME, et al. The completeness of AIDS case reporting, 1988: a multisite collaborative surveillance project. Am J Public Health 1992;82:1495-9.

  6. CDC. HIV/AIDS surveillance report. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, 1997. (Vol 8, no. 1).

  7. Meyer PA, Jones JL, Garrison CZ. Completeness of reporting of diagnosed HIV-infected hospital inpatients. J AIDS 1994;7:1067-73.

  8. Gostin LO, Lazzarini Z, Neslund VS, Osterholm MT. The public health information infrastructure: a national review of the law on health information privacy. JAMA 1996;275:1921-7.

* Reporting in Maryland is exempted for nonstate residents; persons who are tested at anonymous test sites; are blood, semen, or tissue donors; and participants of certain research projects. No exemptions to reporting exist in Texas. 

** HIV-infected persons with a CD4+ T-lymphocyte count of less than 200 cells/uL meet the 1993 expanded AIDS surveillance case definition and are reportable by name for AIDS surveillance.

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TABLE 1. Number of reports of HIV infection and percentage of reports that included data elements for unique identifiers (UIs),
by reporting period -- Maryland (MD) and Texas (TX), July 1994-December 1996
Reports/Data  element    State     July- Dec.      Jan.- June       July- Dec.      Jan.- June       July- Dec.    Overall
                                      1994            1995             1995            1996             1996
Total no. reports         MD         2,238            1,691           1,866            1,881           2,295         9,971
                          TX*        3,932            3,399           3,597            2,852           2,339        16,119
Data element+
Social Security number    MD          69.6            73.1             81.2            83.5             84.5         78.4
                          TX          56.7            68.6             65.0            69.5             75.2         66.0

Date of birth             MD          95.2            96.3             98.7            99.3             98.8         97.6
                          TX          88.4            89.8             93.1            96.8             97.6         92.6

Sex                       MD          96.8            97.2             98.7            99.2             99.4         98.3
                          TX          91.5            97.5             98.4            99.1             97.9         96.6

Race/Ethnicity            MD          85.8            88.5             91.6            94.0             89.9         89.8
                          TX          80.8            91.6             94.4            97.1             95.4         91.1

% Reports with full UI    MD          61.3            65.9             74.9            78.5             76.5         71.4
                          TX          51.8            61.9             61.6            66.5             71.3         61.6
* Excludes approximately 7000 records that had three or more missing UI data elements.
+ Proportion of all reports containing specific UI data elements.

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TABLE 2. Percentage completeness of HIV-infection reporting, availability of unique identifier
(UI) data elements in alternate databases, and sources of report -- Maryland and Texas, July
1994-December 1996
Characteristic                                           Maryland (n=9,971)   Texas (n=16,119)
Completeness of reporting
HIV*                                                            50.4                26.0
CD4+ T-lymphocyte count*                                        44.4                 NA+
HIV&                                                            52.3                 NA
Availability of UI data elements in alternate
Birth@                                                           No                  No
Death                                                           Yes                 Yes
Sexually transmitted disease                                     No                  No
Tuberculosis                                                     No                  No
Drug assistance**                                               Yes                 Yes
Medical assistance++                                            Yes                  No
Hospital discharge                                               No                  No
Source of HIV report
Public                                                          30%&&               77%&&
Private                                                         70%@@                23%***
*   AIDS cases reported through July 1997 compared with the UI database.
+   Not available.
&   HIV cases diagnosed from July 1995 through June 1996 in HIV counseling and testing sites
    compared with the UI database.
@   Used for pediatric AIDS surveillance only.
**  Federal- and state-funded medication program.
++  Federal- and state-funded medical assistance program.
&&  Includes local health departments and state laboratory.
@@  Includes community based organizations and private clinics and laboratories.
*** Includes community bases organizations, hospitals, private physicians, clinics, and

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