Measles—United States, 1997 FREE

MMWR. 1998;47:273-276

2 figures omitted

During 1997, a provisional total of 138 confirmed measles cases was reported to CDC by local and state health departments, the lowest number of measles cases ever reported in 1 year and a 55% decrease from the previous record low of 309 cases reported in 1995. This report describes the epidemiology of measles in the United States in 1997, which suggests that no endemic measles virus is circulating in the United States.

Reported measles cases are classified as imported or indigenous based on where transmission of measles virus is likely to have occurred. Cases in persons who traveled outside the United States within 18 days before rash onset are classified as international importations. Indigenous measles cases are classified into three groups: (1) cases linked epidemiologically to a known international importation, (2) cases in which a measles virus strain is isolated that has been associated with other countries,¹ and (3) all other cases in which no association to an importation was detected.

Of the 138 cases reported in 1997, a total of 57 (41%) were international importations. Thirty-six (63%) occurred in visitors traveling to the United States from other countries. The remaining 21 imported cases occurred in U.S. residents who were abroad during the exposure period. The countries from which measles was most frequently imported were Germany (nine cases), Italy (nine), Switzerland (five), Brazil (five), and Japan (four).

Of the 81 indigenous cases, 17 (21%) cases were linked epidemiologically to international importations. The maximum number of cases epidemiologically linked to a single imported case was four. The longest reported chain of measles transmission following an imported case lasted 5 weeks. Measles virus was isolated from two chains of transmission that included seven (9%) of the 81 indigenous cases; the isolated measles strains have been associated with disease in other countries.¹ There was no epidemiologic link or virologic evidence suggesting importation for the remaining 57 (70%) of the 81 indigenous cases. In 1997, there was epidemiologic or virologic evidence of an international source for 81 (59%) of the 138 cases reported to CDC, compared with 15% in 1995 and 28% in 1996.

In 21 states, no measles cases were reported for 1997, and in 20 states and the District of Columbia, fewer than five cases were reported. Nine states (Arizona, California, Florida, Massachusetts, Minnesota, New York, Pennsylvania, South Dakota, and Texas) accounted for 64% of total cases and 56% of imported cases.

The maximum number of reported cases occurring in a single week was 11, and the median number of cases per week was two. In 9 weeks, no reported cases occurred, and in 21 weeks, all reported cases were associated with imported cases.

The predominant age groups with confirmed measles were preschool-aged children (1-4 years) (40 [29%] cases), followed by persons aged 5-19 years (39 [28%] cases), and persons aged 20-39 years (36 [26%] cases). Of the 138 patients, 32 (23%) had a documented history of vaccination with measles-containing vaccine (MCV): 25 (18%) patients had received one dose of MCV, and seven (5%) had received two doses of MCV. The remaining 106 (77%) patients reported being unvaccinated. For all persons with reported measles in age groups for which vaccine is recommended, 62% were unvaccinated.

A total of 13 outbreaks, defined as three or more epidemiologically linked cases, were reported to CDC by 11 states. Outbreak-related cases accounted for 44% of all cases. The largest outbreak involved eight cases (median: four; range: three to eight cases). Adult/postschool-related and preschool-related outbreaks were the most common, with four outbreaks each, and three outbreaks involved persons with philosophic or religious objections to vaccination. One school-related and one college-related outbreak also were reported. Five (38%) of the 13 outbreaks had known international sources.

State and local health depts. Measles Virus Section, Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Measles Elimination Activity, Child Vaccine Preventable Disease Br, Epidemiology and Surveillance Div, National Immunization Program, CDC.

The 138 confirmed measles cases in 1997 represent a record low since measles became a nationally reportable disease in 1912. Since the 1989-1991 measles resurgence, the number of reported measles cases has declined substantially, with record low numbers reported during 1993-1997 and <500 cases reported during 1993, 1995, and 1997.

The isolated geographic distribution of measles cases, the small number of reported measles cases, and the lack of a recurrent viral strain suggest that there is no endemic circulation of measles virus in the United States.¹ The current pattern of reported measles cases suggests continual importations of measles virus resulting in short chains of secondary transmission in the United States. Some of the indigenous cases that were not associated with importation may have resulted from incomplete reporting and undetected transmission in these chains. Others may have been associated with exposure to undetected importations, or may have been misclassified resulting from false-positive laboratory tests.

Limited secondary transmission following international importation demonstrates the success of vaccination efforts in the United States in increasing population immunity. The measles vaccine coverage rate among children aged 19-35 months was 91% in 1996,² and second-dose coverage is increasing among school children through expanding implementation of school requirements for two doses of measles vaccine. However, there are still groups in the population with low measles immunity. The groups most likely to be vulnerable to measles include those with religious or philosophic objections to vaccination, students in grades not required to have two doses of measles vaccine, health-care workers, and preschool-aged children in areas with low vaccination coverage.^3,4 The exposure of such groups to an imported case could result in large outbreaks. Continued promotion of vaccination, better implementation of the two-dose vaccination requirement, and improved vaccination of health-care workers should decrease the risk for potential outbreaks among these groups.

Permanent elimination of indigenous transmission of measles in the United States will require strong surveillance and high levels of population immunity. Cooperation with other countries to enhance control of measles can reduce the burden of measles in those countries and the risk for importations to the United States. The decrease in importations to the United States from other countries in the Americas following measles elimination efforts underscores the benefits of coordinated measles elimination efforts in the region.⁵ For example, only five importations from elsewhere in the Americas were detected in 1997 (compared with 242 cases in 1990) after increased efforts in measles control.⁶

The Pan American Health Organization established the goal of eliminating measles from the Western Hemisphere by 2000, and the Eastern Mediterranean Regional Office of the World Health Organization (WHO) established a regional goal of measles elimination by 2010. The European Regional Office of WHO is considering establishing a measles elimination goal. Elimination of measles from other regions of the world greatly reduces the risk for importation and spread of measles in the United States. The goal of global elimination is being considered but has not yet been established.

References 6 available.

MMWR. 1998;47:309-314

2 tables, 1 figure omitted

Recent reports based on acquired immunodeficiency syndrome (AIDS) surveillance data have highlighted substantial declines in AIDS incidence and deaths. As a result of improvements in treatment and care of persons infected with human immunodeficiency virus (HIV), surveillance of AIDS alone no longer accurately reflects the magnitude or direction of the epidemic.¹ Current public health and clinical recommendations promote early diagnosis and treatment of HIV disease.² Data on persons in whom HIV infection is diagnosed before AIDS is diagnosed are needed to determine populations in need of prevention and treatment services. This report examines data for persons aged ≥13 years in whom HIV infection was diagnosed in 25 states that conducted name-based HIV surveillance in addition to AIDS surveillance during January 1994-June 1997.* Provisional data indicate that declines in AIDS incidence in these states were not accompanied by comparable declines in the number of newly diagnosed HIV cases.†

In late 1993, the states included in this analysis merged data from the name-based HIV and AIDS case reporting systems into an integrated HIV/AIDS surveillance system. Patient and provider names were deleted before states forwarded data to CDC and replaced by codes. Cases were divided into two mutually exclusive categories: persons in whom HIV infection was diagnosed (without an AIDS diagnosis) and persons in whom HIV infection was diagnosed only when they first had AIDS diagnosed. Data for persons aged ≥13 years were analyzed by the earliest date of diagnosis of HIV or AIDS for January 1994-June 1997. Quarterly trends in the number of persons whose initial diagnosis was HIV infection were compared with quarterly trends in the number of persons whose initial diagnosis was AIDS. HIV and AIDS data were adjusted for delays in reporting of cases and deaths.³

From January 1994 through June 1997, HIV or AIDS was diagnosed in 72,905 persons aged ≥13 years in the 25 states. Of these, HIV infection was the initial diagnosis in 52,690 (72%) and AIDS was the initial diagnosis in 20,215 (28%). From 1995 to 1996, the number of persons in whom HIV infection was the initial diagnosis declined 2%, and the number of persons in whom AIDS was the initial diagnosis declined 9%.

Of 52,690 persons in whom HIV infection was the initial diagnosis, 28% were women, 57% were non-Hispanic blacks, and 18% were infected through heterosexual contact. Among selected demographic groups, the number of persons in whom HIV infection was the initial diagnosis during 1995 compared with 1996 declined 3% among men (from 10,762 to 10,395) but increased 3% among women (from 4126 to 4253). The number of persons in whom HIV infection was the initial diagnosis increased 10% among Hispanics (from 971 to 1070) and decreased 3% among non-Hispanic blacks (from 8569 to 8300) and 2% among non-Hispanic whites (from 5093 to 4966). Men who have sex with men (MSM) accounted for the largest proportion of the HIV diagnoses (32%). Analysis of trends by risk/exposure category is complicated by the high proportion of HIV cases with unreported risk (28%).

Of 52,690 persons in whom HIV infection was the initial diagnosis, 7200 (14%) were aged 13-24 years. The number of HIV diagnoses per quarter-year was approximately constant in this age group, declining 4% from 1995 to 1996 (from 2066 to 1991). Of persons in this age group, 3203 (44%) were female, 4566 (63%) were non-Hispanic black, and 394 (5%) were Hispanic; by risk category, 2270 (31%) were MSM, 1886 (26%) acquired HIV through heterosexual contact, and 449 (6%) were injecting-drug users; 1074 (15%) had AIDS subsequently diagnosed. An additional 653 persons aged 13-24 years had AIDS initially diagnosed.

State and local health departments; Div of HIV/AIDS Prevention—Surveillance, and Epidemiology, National Center for HIV, STD, and TB Prevention, CDC.

The data from these 25 states indicate that from 1994 through mid-1997, the number of persons in whom HIV infection was the initial diagnosis was stable and declines over the entire period were slight. Compared with reported declines in AIDS incidence nationally,¹ these data suggest that HIV incidence was relatively stable in these states. In particular, the number of new HIV diagnoses among persons aged 13-24 years probably more closely indicate HIV incidence trends because young persons have more recently initiated high-risk behaviors.

HIV surveillance data include persons who were infected more recently than were persons reported with AIDS, and their characteristics indicate more recent trends in HIV transmission. Many of the new HIV diagnoses in these states occurred among blacks, women, young MSM, and persons infected through heterosexual contact with substantial increases observed among Hispanics. The HIV case data from these states reflect the changing demographic and risk profile of an epidemic that disproportionately affects racial/ethnic minorities.^1,3 Race/ethnicity is not a risk factor for HIV infection but is likely a marker for other factors that may be predictive of increased risk for HIV infection (e.g., low income, lack of education, and higher rates of injecting and non-injecting drug use).⁴ Black and Hispanic persons who engage in high-risk sex or drug-using behaviors should be a major focus of HIV-prevention efforts, including strategies to promote knowledge of HIV status through voluntary test seeking and to facilitate entry to care and treatment.

Of persons in whom HIV infection was the initial diagnosis, 14% were adolescents and young adults aged 13-24 years, compared with 3% of persons in whom AIDS was the initial diagnosis. This age group is an important target for HIV prevention efforts because a large proportion of all new HIV infections occur among persons in this age group.⁵ In particular, reduction of high-risk sexual behaviors among adolescent and young adult women and MSM is needed to reduce HIV transmission in this age group.

In the 25 states, declines in the number of cases were larger among persons in whom AIDS was the initial diagnosis than among those in whom HIV infection was the initial diagnosis. Most persons with HIV had been tested in a medical facility or other clinical-care setting and had had an opportunity for early treatment interventions to delay HIV-related morbidity and mortality, contributing to declines in AIDS incidence.⁶ In the future, AIDS surveillance data will increasingly reflect access to testing and response to therapy in the population. Approximately one fourth of all new diagnoses in these states occurred among persons who had already developed AIDS when HIV infection was first diagnosed. AIDS surveillance data should be used to target underserved populations for early testing and prompt referrals for treatment.

HIV and AIDS surveillance data mostly reflect the characteristics of persons tested in medical care and other confidential settings. These data may not represent the characteristics of all persons with HIV infection because persons tested anonymously are not reported to the surveillance system, and some persons with HIV infection have not been tested. However, approximately 140,000 persons living with HIV have already been reported and characterized, representing most prevalent infections in these states.⁷ The degree to which integrated HIV and AIDS surveillance data are representative of all infected persons is expected to increase over time as the proportion of untested persons decreases.

The public health usefulness of the HIV surveillance data is affected by the performance of the system of case reporting and follow up.⁸ In these 25 states, most of which require laboratory-based reporting of HIV-positive test results, HIV reporting was very complete. Only 12% of persons in whom HIV infection was the initial diagnosis had not been reported to CDC as an HIV case before being reported as an AIDS case. CDC estimates that <2% of HIV cases are duplicates based on matching of the national coded surveillance database. CDC has developed methods for estimating the risk distribution for AIDS cases with unreported risk³; however, similar methods for HIV cases are not yet available. In this report, the proportion of HIV cases by risk/ exposure categories is an underestimate until follow up is completed for cases reported without risks.³ Name-based HIV reporting should facilitate epidemiologic follow up to increase the completeness of risk/exposure, clinical, treatment, and other data relevant to effective HIV-prevention community planning.

This report highlights the continued need for effective HIV and AIDS prevention programs to reduce rates of HIV transmission and demonstrates the usefulness of integrated HIV and AIDS surveillance data to direct these efforts. State and local areas without such surveillance have limited ability to monitor local changes in HIV infection and disease trends. In these areas, approximately 200,000 persons have had HIV diagnosed (without AIDS),⁷ but data are not available to describe trends in new HIV diagnoses. Implementing integrated HIV and AIDS surveillance in these states and local areas is necessary to provide accurate information for targeting resources to populations most affected (e.g., adolescents, women, racial/ethnic minorities, and young MSM) and for evaluating program effectiveness.

*Alabama, Arizona, Arkansas, Colorado, Idaho, Indiana, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Nevada, New Jersey, North Carolina, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Utah, Virginia, West Virginia, Wisconsin, and Wyoming.

† Single copies of this report will be available until April 24, 1999, from the CDC Prevention Information Network, P.O. Box 6003, Rockville, MD 20849-6003; telephone (800) 458-5231 or (301) 519-0459.

MMWR. 1998;47:315

CDC AND Emory University will cosponsor an applied epidemiology course designed for practicing state and local health department professionals. This course, "Epidemiology in Action," will be held at CDC during November 2-13, 1998. The course emphasizes the practical application of epidemiology to public health problems and comprises lectures, workshops, classroom exercises (including actual epidemiologic problems), roundtable discussions, and computer labs. Topics covered include descriptive epidemiology and biostatistics, analytic epidemiology, epidemic investigations, public health surveillance, surveys and sampling, computers and Epi Info software, and discussions of selected prevalent diseases. There is a tuition charge. Applications must be received by September 11, 1998. Additional information and applications are available from Department PSB, Rollins School of Public Health, Emory University, 7th floor, 1518 Clifton Road, N.E., Atlanta GA 30322; telephone (404) 727-3485; fax (404) 727-4590; or email ogostan@sph.emory.edu.