Epidemiological Profile of HIV/AIDS in Minnesota
Risk Factors among Reported Cases
Mode of Transmission among HIV/AIDS Cases in Minnesota
Since the beginning of the HIV epidemic, the majority of HIV/AIDS cases in Minnesota have been among males with MSM being the predominant mode of exposure reported. Until 2009, both the number and proportion of new HIV infections attributed to MSM had been fairly stable with peaks in 2005 and 2008 (Figure 1).
However, in 2009 the number of newly reported infections among MSM increased by 23 percent compared to 2008. Although the number of new infections among MSM decreased to 178 in 2010 and decreased again to 156 in 2011, the number is still higher than the average of 143 cases between 2002 and 2008. On a much smaller scale, the number of male cases attributed to IDU, MSM/IDU or heterosexual contact has remained stable at about 6, 12 and 9 cases, respectively. In 2011, the number of new male cases attributed to IDU decreased to a record low of 1 case. The number of new male cases attributed to MSM/IDU in 2011 decreased to 7 cases from 10 cases in 2010. The number of male cases attributed to heterosexual contact was 12 in 2011. Additionally, the number of male cases with unspecified risk has fluctuated over the past decade, but has been generally decreasing since 2007 (Figure 2).
Throughout the epidemic, heterosexual contact has been the predominant mode of HIV exposure reported among females in Minnesota (Figure 3). IDU is the second most common mode of transmission among women making up 1 percent of cases among women in 2011. In 1998, 18 percent of women diagnosed with HIV infection did not have a specified mode of transmission. This percentage decreased to 12 percent in 2011 from 24 percent in 2010.
Cases can have unspecified risk for two reasons. The first is that the person has not yet been interviewed or has refused an interview by a Disease Intervention Specialist (DIS) from MDH, and therefore we have little information on their risk category. Disease Intervention Specialists have reported difficulty interviewing recent cases due to language and cultural barriers, as well as difficulty locating the individuals (37 percent of assigned cases diagnosed in 2011 were not interviewed). Second, the person may have no obvious risk. However, heterosexual contact as a mode of HIV transmission is only assigned when the person knows that their partner was HIV-infected or at increased risk for HIV. Often this level of knowledge about sexual partners (anonymous, casual, or exclusive) may be unknown. According to a study conducted by the CDC, it is likely that at least 80 percent of women with unspecified risk acquired HIV through heterosexual contact (Lansky et al., 2001).
In 2004, MDH began estimating mode of exposure for cases with unspecified risk in its annual PowerPoint summary slides (posted on the MDH website). In 2011, estimation was done by using the risk distribution for cases reported between 2009 and 2011 with known risk by race and gender and applying the distribution to those with unspecified risk of the same race and gender. For females a step was added in 2007, whereby females that were interviewed by a DIS and determined not to have any risk other than heterosexual exposure were designated as having heterosexual mode of transmission. There are two exceptions to this method, African-born cases and Asian/Pacific Islander women. For both African-born and Asian/Pacific Islander women, a breakdown of 95 percent heterosexual risk and 5 percent other risk was used. For African-born males, a breakdown of 5 percent male-to-male sex, 90 percent heterosexual risk, and 5 percent other risk was used. These percentages are based on epidemiological literature and/or community experience (1).
(1) Detailed methodology available in the HIV Surveillance Technical Notes
The proportion of cases attributable to a certain mode of exposure differs not only by gender, but also by race. All of the numbers presented in the tables below are based on the estimated mode of exposure using the method mentioned above. Of the new HIV infections diagnosed among males between 2009 and 2011, MSM or MSM/IDU were estimated to account for 96 percent of cases among White males, 95 percent of cases among Hispanic males, 82 percent of cases among African American males, and 16 percent of cases among African-born males. Additionally, heterosexual contact was estimated to account for 80 percent of cases among African-born males, compared to 12 percent and 2 percent for cases among African American and White males, respectively (Table 1). While mode of exposure was estimated for cases among Asian/Pacific Islander and American Indian men, the number of cases for the years 2009-2011 was insufficient to make generalizations regarding risk (less than 20 cases in each group).
|Table 1. New HIV Infections Among Men by Race/Ethnicity and Estimated Mode of Exposure*,
Minnesota - Diagnosis Years 2009 - 2011 Combined
|Mode of Exposure|
* Mode of Exposure numbers have been estimated using cases for 2007-2009 with known risk. For more detail see the HIV Surveillance Technical notes.
Heterosexual contact with a partner who has or is at increased risk for HIV infection is estimated to account for 90 percent of cases among White females during 2009-2011, 98 percent of cases among African American females, and 97 percent of cases among African-born females (Table 2). IDU was estimated to account for 10 percent of cases among Whites, 0 percent among African Americans, and 0 percent among African-born. While mode of exposure was estimated for cases among Hispanic, Asian/Pacific Islander and American Indian women, the number of cases for the years 2009-2011 was insufficient to make generalizations regarding risk (less than 20 cases in each group).
|Table 2. New HIV Infections Among Women by Race/Ethnicity and Estimated Mode of Exposure*, Minnesota - Diagnosis Years 2008 - 2010 Combined|
|Mode of Exposure|
* Mode of Exposure numbers have been estimated using cases for 2008-2010 with known risk. For more detail see the HIV Surveillance Technical notes.