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Incidence and Diagnoses of HIV Infection -- Puerto Rico, 2006

June 5, 2009

In 2006, 33 U.S. states and five territories had confidential, name-based, human immunodeficiency virus (HIV) infection reporting; among territories, Puerto Rico had the second highest rate of HIV infection.1 To characterize the HIV epidemic in Puerto Rico in 2006 (the year with the most recent available data), the Puerto Rico Department of Health and CDC analyzed data on diagnoses of HIV infection (including infections that occurred in 2006 and in previous years) and used a stratified extrapolation approach developed by CDC2 to generate HIV incidence estimates (the number of persons newly infected with HIV in 2006). The results indicated that, in 2006, an estimated 1,440 persons aged >13 years were newly infected with HIV in Puerto Rico, resulting in an estimated incidence rate of 45.0 cases per 100,000 population, twice the rate for the 50 U.S. states and District of Columbia (DC). Males accounted for 65% of new HIV infections in Puerto Rico, and 38% of new HIV infections occurred among persons aged 30-39 years; 39% of new infections were associated with injection-drug use, and 37% with high-risk heterosexual contact. The results provide insight into HIV transmission patterns in Puerto Rico that can help guide allocation of resources and the planning, implementation, and evaluation of HIV prevention programs and other services.

Calculation of diagnoses of HIV infection (i.e., HIV diagnosed with or without a concurrent or later acquired immunodeficiency syndrome [AIDS] diagnosis) was based on the 1,021 diagnoses in 2006 among persons aged >13 years reported to CDC by the Puerto Rico Department of Health through June 2007. Data were categorized by sex, age group, and mode of HIV transmission. The following hierarchy was used for HIV transmission categories: 1) male-to-male sexual contact, 2) injection-drug use, 3) male-to-male sexual contact and injection-drug use, and 4) high-risk heterosexual contact (i.e., with a sex partner known to have or to be at high risk for HIV infection). The number of reported diagnoses was adjusted for reporting delay using a previously reported procedure.3 In addition, for diagnosed cases missing transmission category (32%), a multiple imputation procedure was used.4 Percentages were calculated for sex, age group, and transmission categories. HIV diagnosis rates per 100,000 population were calculated for sex and age group using post-census estimates for 2006.5

HIV incidence for Puerto Rico was calculated using the stratified extrapolation approach.2,6 Remnant diagnostic serum specimens from persons aged >13 years and diagnosed with HIV infection in 2006 in Puerto Rico were tested with the BED HIV-1 capture enzyme immunoassay (BED) to classify infections as recent or long-standing. In addition to the BED result, the estimation method requires HIV testing history, demographic data, and behavioral information for persons with HIV infection diagnosed in 2006. HIV incidence was calculated from cases based on the 1,021 diagnoses of HIV infection, adjusted to 1,460 for reporting delays in 2006. Percentages were calculated for sex, age group, and transmission categories. HIV incidence rates per 100,000 population were calculated for sex and age group using official post-census estimates for 2006.5

In 2006, after adjustment for reporting delays, 1,460 persons aged >13 years were diagnosed with HIV infection in Puerto Rico (Table 1). Of these, 1,036 (71%) were males and 424 (29%) were females. By age group, the greatest number of diagnoses of HIV infection occurred among those aged 30-39 years, followed by those aged 40-49 years. Among males, the most common mode of HIV transmission was injection-drug use (40%), followed by male-to-male sexual contact (30%). Among females, the most common mode of HIV transmission was high-risk heterosexual contact (73%), followed by injection-drug use (27%). The rate of diagnosis of HIV infection in Puerto Rico in 2006 was 45.5 per 100,000 population.

An estimated 1,440 persons (45.0 per 100,000 population) were newly infected with HIV in 2006. The HIV incidence rate among males (62.0) was twice that among females (29.8). The highest rate of incident HIV infections, among persons aged 30-39 years (103.6), was 1.7 times that of the age group with the next highest rate (40-49 years [59.3]). The mode of transmission with the greatest number of new HIV infections was injection-drug use (39%), followed by high-risk heterosexual contact (37%) and male-to-male sexual contact (24%) (Table 2).

Reported by: S Miranda, MPH, B Lopez, MS, EJ García-Rivera, MD, Puerto Rico Dept of Health. M Rangel, MD, PhD, Public Health Strategic Health Care Group, Dept of Veterans Affairs. AL Hernandez, MD, L Espinoza, DDS, Q An, MS, R Song, PhD, R Zhang, MS, Z Myles, MPH, Div of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, CDC.

Editorial Note

These estimates of HIV incidence in Puerto Rico in 2006 reveal important differences between HIV epidemiology in Puerto Rico and the 50 U.S. states and DC. The overall HIV incidence rate in Puerto Rico in 2006 (45.0 per 100,000 population) was twice the estimated U.S. rate (22.8) and 1.5 times the estimated rate for Hispanics in the United States (29.4). The incidence rate among males in Puerto Rico (62.0) was 1.8 times the rate among U.S. males (34.3) and 1.4 times the rate among U.S. Hispanic males (43.1). The incidence rate among females in Puerto Rico (29.8) was 2.5 times the rate among U.S. females (11.9) and 2.0 times the rate in U.S. Hispanic females (14.4).6,7 However, comparisons between the rates for Puerto Rico and the rates for Hispanics in the United States should consider differences in the two populations. Hispanics in the United States include persons who are U.S. born and those of diverse national origin whose behavioral characteristics might differ from Hispanics in Puerto Rico.8 In addition, the number of diagnoses of HIV infection generally is higher in metropolitan areas, and population density in Puerto Rico (1,112 persons per square mile) is 14 times that of the United States (79.6 persons).1,6,7,9

Injection-drug use continues to be the most common mode of HIV transmission in Puerto Rico, whereas most new HIV infections in the 50 U.S. states and DC are attributed to male-to-male sexual contact.1,6-8 Previous reports have indicated greater prevalence of injection-drug use and high-risk health behaviors related to injection-drug use (e.g., frequency of injecting and sharing syringes and other drug paraphernalia) in Puerto Rico than in the United States.8

In 2006, most new HIV infections in the United States, including among Hispanics, occurred in persons aged 13-29 years.7 In contrast, most new HIV infections in Puerto Rico occurred among persons aged 30-39 years. This age group had the highest rates of new HIV infection in both Puerto Rico and the United States; however, the incidence rate in Puerto Rico (103.6 per 100,000 population) was 2.4 times the rate in the United States (42.6).6 One possible explanation for the higher rates in this age group in Puerto Rico might be related to injection-drug use. Persons commonly begin using noninjection drugs and progress to injection-drug use. However, further investigation is needed to test that hypothesis and fully understand the reasons for difference in the rates.

The findings in this report are subject to at least two limitations. The classification of cases reported without a risk factor for transmission was based on a model incorporating random variations to impute missing values.4 Although multiple imputation procedures are designed to maintain associations within the data, the degree of uncertainty introduced by this imputation procedure is unknown. Second, the stratified extrapolation approach to HIV incidence estimation is based on several key assumptions, including that information on previous tests and BED results were missing at random, that testing behavior has not changed substantially over several years, that testing and infection are independent, and that information on previous testing is accurate.2 Concerns have been raised about the accuracy of the BED test, which appeared to result in overestimation of recent HIV infections in Africa and Thailand.10 The implications of these assumptions on incidence estimation have been discussed extensively.2,6

The HIV epidemic in Puerto Rico is notably different from the epidemic in the United States overall and among Hispanics in the United States.1,6-8 CDC supports prevention efforts that target populations at greatest risk in Puerto Rico, including injection-drug users, women who have high-risk heterosexual contact, men who engage in male-to-male sexual contact, and youths. To address transmission of HIV infection among injection-drug users, the Puerto Rico Department of Health provides syringe exchange programs and rapid HIV testing, has implemented policies to allow pharmacies to sell syringes without medical prescription, and provides drug rehabilitation services throughout the country. The findings in this report help describe the HIV epidemic in Puerto Rico and can help guide future allocation of resources and planning, implementation, and evaluation of HIV prevention programs and services.

Acknowledgments

This report is based, in part, on contributions by AL Rivera, I Santiago, V Aviles, MS, M Cruz, MS, B Resto, Y Ayala, and MR Irizarry, Puerto Rico Dept of Health; J Prejean, Div of HIV/AIDS Prevention Surveillance and Epidemiology, M Ayala-Perales, and J Andia, Div of HIV/AIDS Prevention Intervention Research and Support, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, CDC.

References

  1. CDC. HIV/AIDS surveillance report, 2006. Atlanta, GA: US Department of Health and Human Services, CDC; 2008. Report no. 18. Available at www.cdc.gov/hiv/topics/surveillance/resources/reports/2006report/default.htm.
  2. Karon JM, Song R, Kaplan E, Brookmeyer R, Kaplan EH, Hall HI. Estimating HIV incidence in the United States from HIV/AIDS surveillance data and biomarker HIV test results. Stat Med 2008;27:4617-33.
  3. Green TA. Using surveillance data to monitor trends in the AIDS epidemic. Stat Med 1998;17:143-54.
  4. Harrison KM, Kajese T, Hall HI, Song R. Risk factor redistribution of the national HIV/AIDS surveillance data: an alternative approach. Public Health Rep 2008;123:618-26.
  5. CDC. Bridged-race Vintage 2006 postcensal population estimates for July 1, 2000-July 1, 2006, by year, county, single-year of age, bridged-race, Hispanic origin, and sex. Available at www.cdc.gov/nchs/about/major/dvs/popbridge/datadoc.htm#vintage2006.
  6. Hall HI, Song R, Rhodes P, et al; HIV Incidence Surveillance Group. Estimation of HIV incidence in the United States. JAMA 2008;300:520-9.
  7. CDC. Subpopulation estimates from the HIV incidence surveillance system -- United States, 2006. MMWR 2008;57:985-9.
  8. Espinoza L, Hall HI, Selik RM, Hu X. Characteristics of HIV infection among Hispanics, United States 2003-2006. J Acquir Immune Defic Syndr 2008;49:94-101.
  9. US Census Bureau. United States-States; and Puerto Rico. GCT-PH1. Population, housing units, area, and density: 2000 data set. Census 2000 summary file 1 (SF 1) 100-percent data. Available at http://factfinder.census.gov.
  10. UNAIDS. Statement on the use of the BED assay for the estimation of HIV-1 incidence for surveillance or epidemic monitoring: report of a meeting of the UNAIDS Reference Group for Estimates, Modeling and Projections. Athens, Greece: UNAIDS; 2005. Available at www.epidem.org/publications/bed%20statement.pdf.


Table 1. Adjusted number,* percentage, and rate of diagnosis of human immunodeficiency virus (HIV) infection§ among persons aged >13 years, by selected characteristics -- Puerto Rico, 2006
CharacteristicNo.(%)Rate(95% CI)

Sex

Male

1,036

(71)

68.2

(58.0-78.5)

Female

424

(29)

25.1

(19.4-30.8)

Age group at diagnosis (yrs)

13-29

298

(20)

30.1

(22.3-37.8)

30-39

438

(30)

83.1

(65.1-101.1)

40-49

400

(27)

76.6

(57.0-96.1)

>50

325

(22)

27.8

(20.1-35.3)

Male transmission category

Male-to-male sexual contact**

310

(30)

--

--

Injection-drug use

419

(40)

--

--

Male-to-male sexual contact and injection-drug use

39

(4)

--

--

High-risk heterosexual contact††

267

(26)

--

--

Female transmission category

Injection-drug use

114

(27)

--

--

High-risk heterosexual contact

310

(73)

--

--

Total

1,460§§

(100)***

45.5

(39.8-51.2)

* Numbers result from adjustments of reported case counts for reporting delay. Missing information on transmission category was imputed.

† Per 100,000 population; postcensus estimates from the U.S. Census. Rates for transmission category subgroups were not calculated because population denominators were unavailable.

§ Includes 1) persons with a diagnosis of HIV infection but not acquired immunodeficiency syndrome (AIDS), 2) persons with a diagnosis of HIV infection and a later diagnosis of AIDS in 2006, or 3) persons with concurrent diagnoses of HIV infection and AIDS.

¶ Confidence interval.

** Because of small numbers, persons with both male-to-male sexual contact and injection-drug use were included in this category.

†† Heterosexual contact with a person known to have, or to be at high risk for HIV infection.

§§ Because column totals were calculated independently of subpopulation values, the subpopulation values might not sum to the total.

*** Percentages might not sum to 100% because of rounding.


Table 2. Estimated number,* percentage, and rate of new human immunodeficiency virus (HIV) infections among persons aged >13 years, by selected characteristics -- Puerto Rico, 2006
CharacteristicNo.§(95% CI)%Rate(95% CI)

Sex

Male

940

(650-1,240)

65

62.0

(42.5-81.4)

Female

500

(320-700)

35

29.8

(18.8-40.8)

Age group (yrs)

13-29

390

(230-540)

27

39.0

(23-54.8)

30-39

540

(340-750)

38

103.6

(64.2-143.1)

40-49

310

(140-480)

21

59.3

(26.1-92.5)

>50

200

(70-340)

14

17.4

(6.1-28.8)

Transmission category

Male-to-male sexual contact**

350

(190-520)

24

--

--

Injection-drug use

560

(340-790)

39

--

--

High-risk heterosexual contact††

530

(300-770)

37

--

--

Total

1,440

(1,060-1,830)

100

45.0

(33.1-57.0)

* Numbers are estimates, resulting from adjustments of reported case counts for reporting delay. Missing information on transmission category was imputed.

† Per 100,000 population; postcensus estimates from the U.S. Census. Rates for transmission category subgroups were not calculated because population denominators were unavailable.

§ Rounded to tens.

¶ Confidence interval.

** Because of small numbers, persons with both male-to-male sexual contact and injection-drug use were included in this category.

†† Heterosexual contact with a person known to have, or to be at high risk for HIV infection.




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