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Table 9 Estimation of HIV burden in Guntur district using the two methods

From: A population-based study of human immunodeficiency virus in south India reveals major differences from sentinel surveillance-based estimates

Population category Sentinel surveillance method Population-based study method
  2005 population (15–49 years) HIV prevalence* Number with HIV 2005 population (15–49 years) HIV prevalence† Number with HIV
Urban men 370 005‡ 0.0360 13 320 373 926†† 0.0210 7 852
Urban women 366 235‡ 0.0300 10 987 378 557‡‡ 0.0162 6 133
Rural men 848 207‡ 0.0360 30 535 873 893§§ 0.0157 13 720
Rural women 828 055‡ 0.0300 24 842 880 365¶¶ 0.0170 14 966
Urban men with STI 23 526§ 0.2280 5 364    
Urban women with STI 21 234§ 0.1900 4 034    
Rural men with STI 56 821§ 0.2280 12 955    
Rural women with STI 50 815§ 0.1900 9 655    
Female sex workers 7 003¶ 0.1320 924 9 420*** 0.1320 1 243
Men who have sex with men 300** 0.0645 19    
Prisoners: men     800††† 0.1050 84
Hostel residents: men     5 000‡‡‡ 0.0420 210
Hostel residents: women     5 000‡‡‡ 0.0324 162
Undersampled urban men     14 297§§§ 0.0420 600
Undersampled rural men     30 943§§§ 0.0314 972
Total 2 572 201 0.0438 112 635 2 572 201 0.0179 45 942¶¶¶
  1. *HIV prevalence used in the sentinel surveillance method: HIV prevalence from the antenatal sentinel surveillance of 2005 in Guntur at the medical college clinic applied to urban and rural women 15–49 years old, and 20% higher prevalence than this applied to urban and rural men; 2005 HIV prevalence from the sentinel surveillance STI clinic applied to urban and rural men assumed to get STI annually, and 83.3% of this prevalence applied to urban and rural women assumed to get STI annually; 2005 HIV prevalence from the sentinel sites for female sex workers and men who have sex with men used [6].
  2. †HIV prevalence used in the population-based study method: HIV prevalence for urban and rural men and women used from our population-based study; HIV prevalence in men in prisons assumed as 5 times that in urban men; HIV prevalence in men and women hostel residents assumed as twice the urban prevalence in each sex; HIV prevalence in undersampled urban and rural men assumed as twice the prevalence in sampled urban and rural men.
  3. ‡Excludes men and women shown separately in other categories below.
  4. §In this method, 6% urban men and women, and 6.3% rural men and women were assumed to get STI annually; this portion assumed to cover high-risk groups in the population, excluding female sex workers and men who have sex with men, shown separately [3,6].
  5. ¶0.55% of urban and rural women comprising that portion of female sex workers not expected to be covered in the STI component of the calculations [6].
  6. **This method estimated 5082 men who have sex with men in Andhra Pradesh who were not expected to be covered in the STI component of the calculations (Table 1); for Guntur district we used the fraction proportional to its 5.9% population contribution to the state.
  7. ††Excludes urban men in prisons at a given time, residents of hostels, and undersampled urban men.
  8. ‡‡Excludes urban female sex workers estimated not covered in our population-based sample and residents of hostels.
  9. §§Excludes rural men in prisons at a given time and undersampled rural men.
  10. ¶¶Excludes rural female sex workers estimated not covered in our population-based sample.
  11. ***Our urban and rural women samples included five (0.14%) and four (0.12%) women, respectively, who were identified as sex workers, although other unidentified sex workers would also likely be part of our sample; Guntur district was estimated to have 11000 female sex workers in 2005 [9], 0.86% of women in the 15–49-year age group; based on our previous study of female sex workers in Andhra Pradesh [26,27], we extrapolated that 60% sex workers are in urban areas and 40% in rural areas, suggesting that in Guntur district 6600 sex workers would be urban and 4400 rural; this implied that 6055 urban and 3365 rural sex workers were not represented in our population-based sample, and are therefore shown separately.
  12. ††Estimated based on capacity of prisons in Guntur district, and assumed that half the prisoners are urban and half are rural.
  13. ‡‡We estimated by performing a census of residential hostels for students and working people in the urban areas of Guntur district that 5000 men and 5000 women 18–29 years old, and 7000 boys and 3500 girls 15–17 years old, would be residing in these hostels. The younger age group comprises of students mostly in strictly supervised residential schools, and therefore, their risk of HIV was considered similar to that in the general population; the 18–29-year age group comprises of college students and working people living mostly without any supervision, and therefore, the HIV prevalence for them was considered twice the urban prevalence for each sex. As the estimated number in this latter category was the same for men and women, and in India more young men than women would be expected to be living alone or with others of the same sex, we assessed our sample for the number of 18–29-year-old men and women living alone or with others of the same sex outside the hostel setting and found 76 men (5.8% of urban men sample in this age group) and 14 (1% of urban women sample in this age group) in this category.
  14. §§§Our population-based sample had 3.7% and 3.5% undersampling of urban and rural men, respectively, compared with their ratio to women in the Census data [23]; we considered this undersampled group separately, after excluding prisoners, assuming that these missing men would be at higher risk of HIV.
  15. ¶¶¶Some other groups considered at relatively high risk of HIV, men who have sex with men (including men who sell sex to men), intravenous drug users, and migrant labourers, were not added separately to this calculation for the following reasons. (i) Our population-based sample had 2.1% men who reported having had sex with men, which included 0.26% men who had sold sex to men. In our previous study of 6661 men who had sex with men recruited through extensive snowball sampling in 13 districts of Andhra Pradesh 26.7% had sold sex to men [28,29], which was 0.015% of 15–49-year-old men in these 13 districts; this fraction was 17 times less than the fraction of 0.26% in our population-based sample. The latter would seem to be an adequate representation of this group in our sample if we conservatively assume that we had actually reached only 1/17th of the actual men who sell sex to men in our extensive snowball sampling method in the 13-district study. (ii) The number of intravenous drug users is considered to be negligible in Andhra Pradesh. (iii) We estimated that our stratified random sampling strategy, which had adequate coverage of lower socioeconomic strata, would include migrant labourers residing in the sampled areas for 6 months or more according to their proportion in the population; even if this were not completely so, the addition of undersampled men with assumed higher HIV prevalence to the calculation, as mentioned above, would cover this group.