The National Medical Journal of India; Vol.16: 126-31, No.3, 2003 The Natural History of Adult patients infected with Human Immunodeficiency Virus in Mumbai Hira Subhash K, MD, MPH1/2/5 Shroff HJ,MD3 Lanjewar DN, MD4 Dholkia YN, MD1 Bhatia, Vandana P, MD1 Dupont HL, MD5 1 : AIDS Research and Control Centre (ARCON), Sir J. J. Hospital, Mumbai 2 : Department of Infectious diseases, M. G. M. Medical College, Navi Mumbai 3 : Formerly at Department of Skin & VD, Grant Medical College & Sir J.J.Hospital, Mumbai 4 : Department of Pathology, Grant Medical College & Sir J. J. Hospital, Mumbai 5 : The University of Texas-Houston, USA Word count: 1862 (text only) Corresponding author: Dr. Subhash K. Hira AIDS Research and Control Centre (ARCON) STD Building, Sir J. J. Hospital, Mumbai 400 008. e-mail: subhash_hira@hotmail.com ABSTRACT Background: The natural history studies of untreated HIV infection are useful for clinicians, public health experts and policy makers to improve and monitor care, to plan services and control, and for modelling the epidemic. Several natural history studies have been published in developed countries for gay men and IV drug users. Few studies have emerged for heterosexual populations from Africa. However, India with an emerging epidemic required a similar study. Hence, a study was designed to determine the HIV-disease progression in a prevalent cohort of adult HIV-seropositive patients. Patients and Methods: A prevalent cohort of 1009 patients comprising of 488 asymptomatic HIV seropositive persons, 259 with AIDS-Related Complex (ARC), and 262 with Acquired Immunodeficiency Syndrome (AIDS) were recruited for the study at Sir J. J. hospital in Mumbai. Case control study was conducted to determine the correlation of clinical features and other factors on disease progression. The disease progression from the stage of asymptomatic to that of ARC and AIDS was determined using time series analysis. Also, the incubation period from HIV to AIDS was determined using Weibull curves. Results: The median incubation periods for progression were: HIV to AIDS - 7.9 years and ARC to AIDS - 1.9 years. The median survival after attaining AIDS was 19.2 months. Comparison of progressors and nonprogressors revealed that disease progression was correlated with the clinical features like chronic fever (OR 5.6), persistent generalised lymphadenopathy (OR 4.7), persistent cough of > one month (OR 3.5), chronic diarrhoea (OR 3.3), oral candidiasis (OR 3.2), weight loss of > 10% of the body weight within one month (OR 2.9), incident tuberculosis (OR 2.8), and herpes zoster (OR 2.5). The annual incidence of active clinical tuberculosis was 86/1503 p-y (5.7/100p-y). The median time to occurrence of active tuberculosis was 21.6 months. The annual incidence of mortality was 96/2009 p-y (4.8/100p-y, CI0.95 3.4,6.2). Conclusions: Progression to AIDS and death was faster among heterosexual cohort in Mumbai than that reported for gay men and hemophiliacs in the US and Europe. Strategies need to be developed to prevent the occurrence of tuberculosis among HIV-infected patients because that will help reduce the risk of morbidity and mortality. This is the first large-scale study in the Indian sub-continent where longitudinal followup of HIV-infected persons was performed. The findings will be useful for advocacy and for assessing impact of anti-retroviral therapy in India. Key word(s): HIV/AIDS natural history, incubation period, correlates of disease progression, India. 2 INTRODUCTION: The natural history studies of untreated HIV infection are relevant because these allow a comparison of the disease in different regions of the world. Such studies will continue to be useful for epidemiologists, clinicians and policy makers in developing countries to improve care, planning of services and control, to project the number of AIDS cases, and to assess the impact of anti-retroviral therapy (ART) as most governments of developing countries are still evaluating priority options for phased introduction of ART. Extensive studies of the natural history of HIV infection were conducted among gay men and intravenous drug users in the United States and Europe in mid-80s1-4. There were several other studies, which had established biologic and clinical predictors of HIV-disease progression. The disease progression depends upon the intensity of host immune responses5,6, ability of virus to induce syncytia formation7, prophylaxis for some opportunistic infections such as Pneumocystis carinii and Mycobacterium tuberculosis among others8, and the occurrence of acute HIV stage9. Furthermore, disease progression also depends on a ‘set-point or balance’ that is reached between the degree of viral replication and immune control as determined by the level of circulating virus (viral load)10, the ongoing viral mutations that allow the virus to escape partially effective immune control at future time points11, the high levels of certain cytokines (IL-4,IL-10) released by the activated cells pressure the immune response towards a less effective antibody response12, and the recent introduction of ART13. The natural history studies in the United States and Europe were conducted predominantly among blood transfusion recipients or gay men; hence, have limited application to developing countries where primary mode of transmission is heterosexual. Recent studies on natural history come from Uganda and Haiti, where the population under study was heterosexual14-17. This study of natural history among heterosexual population is first of its kind in India and in the Asian region. Patients and Methods: Between April 1994 and December 2000, 3510 patients referred with clinical features 3 suggestive of immune suppression or those with clinical evidence of sexually transmitted infections (STI) referred to AIDS Research and Control Centre (ARCON) at Sir J. J. Hospital in Mumbai were screened for the natural history study. Detailed demographic and sexual histories were obtained. Thorough clinical and genital examinations were performed. Prior to investigation, all patients were offered pre-test counselling by trained clinical psychologists. The laboratory investigations included full blood count, ESR, liver and renal function tests, ELISA for HIV-1/2 (Sanofi Pasteur, France) and those found positive were re-tested with Genodia (Serodia, Japan). Western blot (Genelab, Singapore) was performed on 1009 patients who were followed for more than 6 months and formed the final cohort for this study. Routine RPR test for syphilis and confirmation of positives with TPHA (Glaxo-Wellcome) and testing for CD4/CD8 cell enumeration (Sanofi Pasteur, France) was done. Montoux skin test was performed for all patients18. Using globally standardised definitions of clinical markers described in WHO reference manual 19 , the presence or absence of the clinical markers like weight loss > 10 per cent of the body weight within a month, chronic fever > one month, persistent cough > one month, recurrent diarrhoea > one month, tuberculosis18, oral candidiasis, persistent generalised lymphadenopathy, STI, including genital ulcer diseases (GUD) 20 were recorded at the base line for all patients. Overall, patients were classified either as Asymptomatic HIV sero-positive; AIDS Related Complex (ARC); or AIDS based on clinical definition and CD4 counts21. WHO guidelines for case definition now refer to ARC stage as “intermediate HIV-related illness”. Similarly, laboratory tests and staging were conducted on several follow-up sessions. The final cohort comprised of 488 asymptomatic HIV seropositive persons, 259 with ARC, and 262 with AIDS. The follow-up procedure included several sessions of post-test counselling based on the patients' requirements and as determined by the counsellor(s). Asymptomatic HIV seropositive patients and those with minor non-opportunistic infections were encouraged to return for follow-up visits at 3-month intervals. Those with moderate and serious opportunistic infections (OI) 1,2,5 were provided co-trimoxazole prophylaxis and further treated as outpatients or admitted on the wards based on clinical judgement. Option of prescription of anti-retroviral therapy (ART) costing >Rs.20,000/month was offered to symptomatic and cases of AIDS; however, few were able to 4 afford and were transferred to a different cohort that was being followed on ART. Disease progression was studied in four outcome categories as follows: (1) Asymptomatic to ARC (2) Asymptomatic to AIDS (3) ARC to AIDS (4) AIDS to death. Rate of disease progression to any stage from the proceeding stage was defined as the ratio of number of new entries in that stage and person-years followed. However, this caused some overlap in person-years of followup between outcome categories 1 and 2 because most individuals progress to AIDS through stage of ARC. To evaluate the impact of age, gender, social variables like occupation, education, marital status, sexual orientation, and the clinical features on the risk of HIV progression to higher stages including death, case-control analysis was performed using the time series method. The entire analysis was done using the software packages such as Mathematica22 and Epi-Info 23. The data was analysed with cut-off point of June 2001. Also, to determine the incubation periods for disease progression, the Weibull curve was considered a good fit due to the flexibility of its shapes24. Additionally, truncated Weibull distribution was applied to estimate mean incubation period from HIV to AIDS because exact time of acquisition of HIV infection was not known. In such a situation, truncated Weibull was recommended technique to compensate for missed durations on both sides of the data25. Patient’s anonymity was protected and informed, written and signed consent forms were obtained. The study was approved by the IRB of the Government of Maharashtra (Office of Medical Education and Research), the Dean of Sir J. J. Hospital and an internal ARCON review committee. Results: The prevalent cohort of 1009 patients comprised of 775 (76.8%) males and 234 (23.2 %) females. The cohort comprised predominantly of heterosexual individuals among whom 20% had never attended formal education, one-third were single, two-third gave current history of substance use, and significantly greater number of males had clinical diseases as compared with females. Their demographic, social variables, and the spectrum of clinical features at the time of 5 recruitment in to the study are presented in table 1. Montaux test was negative (0-5mm) in 896 (88.8%), 6-15mm in 71 (7%), and >15mm in 42 (4.2 %). Of the 1009 patients followed for 2009 person-years (p-y); mean 2.0 years (range >0.6<7.0). Three hundred sixty one (17.9/100p-y) of the prevalent cohort progressed to higher stage or death. This progression was not significantly different for all four-outcome categories (table 2). The entire case-control analysis for disease progression was categorised in the following categories: Progression by gender and age Over all, the disease progression among males and females was not significantly different (OR1.1, CI 0.9,1.5;p=0.40) (table 3). Among the cohort, 20% were in 15-24 years age group, 58% were in 25-34 years age group, 18% were in 35-44 age group and remaining 4% were in 44+ age group. The average age of males and females that progressed to AIDS was above 31 years. Evidently, these persons were at the peak of productivity. The multivariate analysis of progressors revealed that the risk of disease progression was not significantly related to their age (Table 4). Progression by Social variables Individuals employed on clerical jobs showed relatively higher rate of disease progression (table 5). Skilled workers, housewives and married men were all at identical risk of disease progression. Also, the literacy level and recent history of substance use was not a significant factor contributing towards the disease progression (OR literates vs illiterates OR1.17; CI 0.95 0.77, 1.91). Progression by clinical and immunologic features Of 1009 persons recruited in the study, 714 did not have evidence of clinical active tuberculosis. The latter were followed for 1503 p-y and 86 incident cases of active tuberculosis were diagnosed (incidence 5.6/100 p-y). Case-control analysis revealed that patients with chronic 6 fever were at highest risk of progression (OR 5.6). Also, the progression was high among patients with the following clinical features in decreasing order of risk: persistent generalised lymphadenopathy (OR 4.7), persistent cough of > one month (OR 3.5), chronic diarrhoea (OR 3.3), oral candidiasis (OR 3.2), weight loss of > 10 per cent of the body weight within one month (OR 2.9), incident tuberculosis (OR 2.8), and herpes zoster (OR 2.5)(table 6). The loss of CD4+ cells in asymptomatic males and females was 55/p-y and 49/p-y, respectively (OR1.2; CI0.95 0.8,1.7). Incidence of mortality: The rate of mortality in the prevalent cohort was 4.8/100p-y (96/2009 p-y). The incidence of AIDS to death was lower possibly due to some deaths being missed because terminally ill patients tend to return to their villages. Incidence of death in the cohort was also studied by controlling for tuberculosis. It was found that 49/96 (51.0%) deaths were directly attributable to incident tuberculosis. Weibull Curve Analysis Figure 1 presents the median time for occurrence of AIDS at 7.6 years using simple Weibull and 7.9 years using truncated Weibull curves. The latter median incubation period did not alter by adding some artificial length of 3, 6, 9, 12,15…. n months to the date of recruitment visit to adjust for the actual dates of HIV infection. This was the advantage of application of truncated Weibull distribution and detailed discussion can be found elsewhere19. The estimated median duration of 1.9 years (22.8 months) from ARC to AIDS and 1.6 years (19.2 months) from AIDS to death are presented in Figures 2 and 3, respectively. The median duration for the occurrence of clinical tuberculosis was 1.8 years i.e. 21.6 months (figure 4). Discussion: This is the first study describing the natural history of HIV infection among heterosexual persons in South-Asia. The cohort comprised of skilled and unskilled workers and housewives. More than 80 per cent of the patients were educated; hence, literacy did not seem to 7 be a deterrent for acquiring the HIV infection. The rate of disease progression was not directly proportional to the age, education, occupation or substance (predominantly tobacco or alcohol) use by the patients. This finding was identical to that of tricontinental seroconverter study26. Also, gender of patients was not an important correlate of disease progression. Identically, the European27 study revealed that after adjusting for age, gender was not a correlate of disease progression. Since the cohort of this study was not exposed to any anti-retroviral therapy, findings of this study will be relevant to the Asian region for some time to come because widespread use of anti-retroviral drugs (ART) is likely to happen in developing countries in a phased manner. Subsequently, these findings will provide historical baseline for determining the impact of ART. The median incubation period for AIDS among gay and bisexual men was reported to be 11.0 years (mean, 11.8 years, 95% confidence interval, 10.6 to 13.0 years) studies on natural history of HIV come from the US and Europe 29-31 28 . Although the best , those results may not be comparable with the Mumbai cohort due to differences in populations among whom studies were done, their nutritional status, the level of tropical endemic infections, their sexual orientations, racial differences in immunity, virus variations, and varied environments. However, median disease progression from HIV infection to AIDS in Mumbai was 7.9 years, which is similar to 9.4 years from HIV to death in the Ugandan natural history study of heterosexual population14-16. Apparently, incubation period for AIDS is shorter in Mumbai. Yet, the median survival of 19 months in Mumbai cohort after attaining AIDS was similar to heterosexual patients in the New York City cohort32. However, the incidence of AIDS to death in our study may be an underestimation due to some deaths being missed because terminally ill patients tend to return to their villages. These findings will be useful for demographers, epidemiologists and policy makers to forecast the impact of the epidemic in Asia. Chronic fever, diarrhoea, oral candidiasis, weight loss, incident tuberculosis, and herpes zoster were seen as significant clinical markers associated with disease progression among the heterosexual cohort in Mumbai. Similar findings for gay men and intravenous drug users were 8 also observed in the Italian and Chilean cohorts27,33. There was temporal association between the occurrence of clinical tuberculosis and death34. The degree of association of these clinical markers with disease progression observed in this study will be useful for clinicians providing care and support to patients with HIV/AIDS. Clinicians will be able to anticipate stages and prepare their patients and families accordingly. The increased availability of anti-retroviral therapy (ART) has significantly altered the natural history and the occurrence of opportunistic infections (OI) in several developing countries. The most striking benefit of ART in South Africa is the 80% reduction in the incidence of HIV-1 associated tuberculosis (95% CI 62,91)13. Studies in Brazil 35 and Chile 36 have shown the declining annual trends for the occurrence of OI after widespread introduction of ART and safe discontinuation of OI prophylaxis. Italian ART studies reported significantly fewer infections and consequent shorter hospital stay 37 and modification of the natural history of cryptosporidiosis and microsporidiosis 38 . With scaling-up of access to ART in India, the findings of this study will provide historical baseline for assessing the impact of ART on the natural history of HIV. Acknowledgement: Authors wish to thank Drs. Arni Srinivas Rao, Clements Fernandes, Malavika Kohli, ARCON and JJ Hospital staff for their inputs in the conduct of this study. The resources for this study were provided by the University of Texas-Houston and the Government of Maharashtra. 9 References: 1. Jaffe HW, Darrow WW, Echenberg DF, O'Malley PM, Getchell JP, Kalyanaraman VS, et al. The Acquird Immunodeficiency Syndrome in a cohort of homosexual men. Ann Inten Med 1985; 103:210-4. 2. Lefrere JJ, Lambin P, Courouce AM, Doinel C. Progression to AIDS in the majority of asymptomatic HIV-infected people. AIDS 1989; 3:603-4. 3. Rezza G, Lazzarin A, Angarano G, Sinicco A, Pristera R, Ortona L, et al. The natural history of HIV infection in intravenous drug users: risk of disease progression in a cohort of seroconverters. 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Table 1: Demographic, Social Factors, and Clinical Features of Natural History Cohort (n=1009) Male Female 14 Total Mean Age (yrs) n=775(%) 30.71 Occupation Trading Unemployed Unskilled Labour Skilled Labour Clerical Professional Student Housewife CSW Not known 47 (6.0) 86 (11.0) 308 (39.7) 229 (29.5) 34 (4.3) 23 (2.9) 4 (0.5) 0 0 44 (5.6) n=234 (%) 26.81 0 n=1009 (%) 29.96 29 (12.4) 2 (0.8) 6 (2.6) 5 (2.1) 1 (0.4) 160 (68.4) 10 (4.3) 7 (0.9) 47 (4.7) 100 (9.9) 337 (33.4) 231 (22.9) 40 (4.0) 28 (2.8) 5 (0.5) 160 (15.9) 10 (0.9) 51 (5.1) Educational Level Nil 114 (14.7) School 388 (50.0) SSC 161 (20.7) HSC 62 (8.0) Graduate 38 (4.9) Post Graduate 8 (1.0) Not known 4 (0.5) 71 (30.3) 106 (45.3) 43 (18.4) 9 (3.8) 4 (1.7) 0 1 (0.4) 185 (18.3) 494 (49.0) 204 (20.2) 71 (7.0) 42 (4.2) 8 (0.8) 5 (0.5) Marital Status Unmarried Married Divorced Widowed Remarriage Not known 273 (35.2) 480 (61.9) 9 (1.1) 11 (1.4) 0 2 (0.2) 16 (6.8) 177 (75.6) 5 ((2.1) 33 (14.1) 1 (0.4) 2 (0.8) 289 (28.7) 657 (65.1) 14 (1.4) Addiction Alcohol Tobacco Smoking Non-IV Drugs IV Drugs Nil Not known 419 (54.0) 108 (13.9) 71 (9.1) 1 (0.1) 2 (0.2) 161 (20.7) 13 (1.7) 10 (4.3) 20 (8.5) 2 (0.8) 2 (0.8) 1 (0.4) 190 (81.2) 9 (3.8) 429 (42.5) 128 (12.7) 73 (7.2) 3 (0.3) 3 (0.3) 351 (34.8) 22 (2.2) Sexuality Heterosexual Homosexual Bisexual Not known 677 (87.4) 9 (1.2) 19 (2.5) 70 (9.0) 213(91.0) 0 1(0.4) 20(8.5) 895 (88.7) 9 (0.9) 20 (2.0) 90 (9.0) 14 (6.0) Presenting Clinical Features 44 (4.4) 1 (0.1) 4 (0.4) OR(CI0.95) 15 Weight loss more than 10 % of the body weight 200 (25.8) 37 (15.8) 237 (23.5) 1.6 (1.1,2.4;p=0.01) 113 (11.1) 1.8 (1.0,3.3;p=0.03) Diarrhoea more than one month 97 (12.5) Fever more than one month 197 (25.4) 43 (18.4) 240 (23.8) 1.4 (0.9,2.0;p=0.07) Cough more than one month 139 (17.9) 28 (12.0) 167 (16.6) 1.5 (0.9,2.4;p=0.06) PGL 73 (9.4) 8 (3.4) 82 (8.0) 2.8 (1.3,6.3;p=0.008) Herpes zoster 121 (15.6) 17 (7.3) 138(13.7) 2.2 (1.3,3.8;p=0.003) Oral candidiasis 83 (10.7) 16 (6.8) 9 (3.8) Tuberculosis 223 (28.8) 33 (14.1) Incident TB 70 (9.0) 16 (6.8) 16 92 (9.1) 2.8 (1.4,6.1;p=0.004) 256(25.4) 2.0 (1.4,3.4;p=0.000) 86 (8.5) 1.3 (0.7,2.4;p=0.33) Table 2: Incidence of progression from recruitment stage to ARC, AIDS, or Death in the prevalent cohort (n=361) Progression category No. Patients Progressed P-Y followed Incidence Rate% (CI 0.95) 1. Asymptomatic to ARC 105 789.94 13.29 (9.89, 16.69) 2. Asymptomatic to AIDS 106 822.56* 12.89 (9.54, 16.23) 3. ARC to AIDS 96 462.61 20.75 (14.53, 26.98) 4. AIDS to Death 54 519.18 10.40 (6.25, 14.55) ___________________ * Person-years overlapping with category 1. Table 3: Incidence of Progression from recruitment stage to ARC, AIDS and Death by Gender (n=361) 17 Progression category Male (/100 p-y) Female (/100 p-y) 1. Asymptomatic to ARC 69/535.1 p-y(12.9) 36/254.9 p-y(14.1) 2. Asymptomatic to AIDS 79/577.9* p-y (13.7) 27/244.7* p-y (11.0) 3. ARC to AIDS 84/393.9 p-y (21.3) 12/68.7 p-y (17.5) 4. AIDS to Death 47/446.2 p-y(10.5) 7/73.0 p-y (9.6) Total progression 279/1953.1p-y(14.3) 82/641.3p-y (12.8) ____________________________________ * Person-years overlapping with category 1 Table 4: Comparison of Incidence of Progression among Age Groups (n=361) Progression Category 15-24 n/p-y(/100p-y) Asymptomatic to ARC 27/69.8(38.7) 25-34 n/p-y(/100p-y) 35-44 n/p-y(/100p-y) 58/134.5(43.1) 18/41.9(43.0) 18 45+ n/p-y(/100p-y) 2/8.3(24.0) Asymptomatic to AIDS 25/63.1(39.6) ARC to AIDS 13/35.5(36.6) 3/8.7(34.7) 15/34.6(43.4) 58/118.3(49.0) 19/36.3(52.3) 4/7.1(56.3) AIDS to Death 5/9.3(53.8) 28/42.9(65.3) Total progression 72/176.7(40.7) 209/475.4(44.0) OR 1.0 65/179.8(36.2) 16/22.0(72.9) 5/12.0(41.7) 66/135.6(48.7) 14/36.1(38.8) 1.1(0.8,1.5) 1.2(0.8,1.8) 0.9(0.5,1.9) Table 5: Incidence of Progression from recruitment stage to ARC, AIDS and Death by social variables (n=361). Progressors Non-progressors OR(CI0.95) N=361 n=626* Trading 16 30 1.0 (0.5,2.0) Unemployed 38 60 1.2 (0.7,2.0) Unskilled labour 121 209 1.1 (0.8,1.60) Skilled labour 78 146 1.00 Occupation 19 Clerical 19 20 1.8 (0.9,3.7) Professional 7 20 0.7 (0.2,1.7) Student 1 4 0.5 (0.0,4.5) Housewife 58 99 1.1 (0.7,1.7) Sex Worker 3 7 0.8 (0.2,3.6) Others/Not known 20 31 Nil 64 117 0.8 (0.5,1.3) School 167 314 0.8 (0.6,1.2) Secondary level 80 121 1.00 High school 29 40 1.1 (0.6,2.0) Graduate 15 27 0.8 (0.4,1.2) Postgraduate 3 5 0.9 (0.2,4.5) Not known 3 2 Unmarried 100 179 1.0 (0.7,1.3) Married 239 407 1.00 Divorced 5 9 1.0 (0.3,3.1) Widowed 15 29 0.9 (0.4,1.8) Others/Not known 2 2 Alcohol 156 266 1.1 (0.8,1.5) Tobacco 48 75 1.2 (0.8,1.9) Smoking 25 45 1.0 (0.6,1.8) Nil 120 225 1.00 Not known 12 15 Educational Level Marital Status Addiction 22 missing values 20 Table 6: Incidence of clinical features among progressors and non-progressors(n=361) Diseases Among Progressors/100p-y Asympt- Asympt- to-ARC to-AIDS ARC- Diseases Among OR(CI0.95) Non-p rogressors (Prog vs to-Death /100p-y Nonprog) AIDS- to-AIDS Clinical Feature Weight loss > 10per cent of body weight 4.7 5.8 6.0 150.2 3.6 2.9(1.9,4.6) Diarrhoea > One month 2.4 2.9 3.6 43.1 1.6 3.3(1.8,6.1) Fever > One month 9.2 6.7 4.1 126.0 1.8 5.6(3.1,10.1) Cough > One month 4.4 5.9 7.8 56.8 2.6 3.5(2.1,5.7) PGL 4.9 0.7 3.0 13.1 0.8 4.7(2.0,11.2) Herpes Zoster 2.0 1.1 0.7 14.7 1.0 2.5(1.1,5.8) Oral Candidiasis 4.0 2.5 9.2 24.6 2.0 3.2(1.8,5.6) Incident 0.4 17.9 16.1 122.6 Tuberculosis 21 5.7 2.8(2.0,4.1) Figure Captions: Figure 1. Estimated incubation period of adult HIV to AIDS in Mumbai. Truncated distribution is plotted with estimated parameters = 0.0340 and =1.4674: Simple distribution is plotted with estimated parameters 1= 0.1200 and 1=0.8680. Figure 2. Estimated duration from ARC to AIDS = 0.2280 and =1.7662 Figure 3. Estimated duration from AIDS to death = 0.2641 and =2.2289 Figure 4. Weibull estimates for the incidence of tuberculosis. = 0.2748 and =1.6603 22 23 Figure 1. Estimated incubation period of adult HIV to AIDS in Mumbai 1 0.9 Cumulative probability 0.8 0.7 Truncated Weibull 0.6 Simple Weibull 0.5 0.4 0.3 0.2 0.1 0 0 5 10 15 20 Years 2 25 30 Figure 2. Estimated duration from ARC to AIDS 1 0.9 Cumulative probability 0.8 0.7 0.6 (Median 1.9 years) 0.5 0.4 0.3 0.2 0.1 0 0 2 4 6 8 10 Years 3 Figure 3. Estimated duration from AIDS to death 1 Cumulative probability 0.9 0.8 0.7 0.6 (Median 1.6 years) 0.5 0.4 0.3 0.2 0.1 0 0 2 4 6 8 10 Years 4 Figure 4. Weibull estimates for the incidence of tuberculosis 1 Cumulative probability 0.9 0.8 0.7 0.6 Median is 1.8 years 0.5 0.4 0.3 0.2 0.1 0 0 2 4 6 8 10 Years 5