Data were obtained from the Cuban HIV/AIDS programme established in 1983 following developments of AIDS epidemics in other countries. The detection of the first HIV-positive person in Cuba took place in December 1985. This person was a heterosexual male returning from travel abroad. The first death due to AIDS occurred in April 1986 and was officially announced in the Cuban press soon after.
This Cuban HIV/AIDS programme included a system to detect HIV cases from several sources. Some of these sources started to be used at the beginning of the programme, others were introduced later and some have been discontinued. Since 1993, this detection system has focused on 6 major sources. These are blood donors, persons treated for other sexually transmitted infections, persons admitted to hospital with suspected HIV infection or subject to specific procedures like dialysis, persons volunteering to be tested, persons whose general practitioner has recommended HIV testing and, lastly, sexual partner tracing (see below). Other sources include testing of all pregnant women and prison inmates.
Since 1990, each time a person is tested for HIV, she/he is informed that such a test is going to be performed. When a person is found to be HIV-positive, the following information is collected and recorded in a national HIV/AIDS database: date of detection, age, gender, area of residence, gender of sexual partners in the past two years. A man having sex with men (MSM) is defined in this paper as a male reporting at least one sexual contact with another man in the past 2 years. From 1986, a person testing HIV-positive is interviewed by health workers using a non-anonymous structured questionnaire. They are invited to give names and contact details of sexual partners of the past two years. These partners are then traced and a recommendation for voluntary HIV testing is made .
Before 1994, persons who tested HIV-positive were followed up by the national health programme in AIDS sanatoria, which generated a lively and controversial debate [6–8]. This programme has evolved from its original conception and an outpatient care system was started in 1994 for those who wanted to leave the sanatoria. By the end of 2003, 60% of HIV-positive persons lived outside the sanatoria . Each HIV-positive person receives, either in the sanatoria or in the outpatient system, regular counselling on living with HIV and how to prevent the risk of transmitting the virus.
AIDS cases are defined by the national health programme as HIV-positive persons with at least one opportunistic infection or, since the year 2000, a CD4 count of less than 200 cells/mm3. When a person is diagnosed with AIDS, the date of diagnosis is reported to the health authorities and added to the national HIV/AIDS database. Dates of death are also recorded in this database.
Antiretroviral therapy (ART) became available in 2000 and today every person with AIDS or every HIV-positive person with a CD4 count of less than 300 cells/mm3 receives ART free of charge. Pregnant women are all tested for HIV and ART is proposed free of charge to pregnant women who test HIV-positive in order to reduce the risk of transmission of HIV to their child.
In this paper, we analyse HIV and AIDS cases recorded yearly in the national HIV-AIDS database. HIV prevalence among adults at the end of a year (y) was calculated as the number of cases of persons living with HIV. Prevalence rates among adults were calculated by dividing the number of HIV cases from the Cuban HIV/AIDS database by the adult population. Confidence intervals for prevalence rates were calculated assuming a binomial distribution.
In this paper, following the Cuban definition, adults were defined as persons aged 15 years or more. The annual prevalence rate among pregnant women was calculated as the number of pregnant women who have tested HIV-positive in one year divided by the total number of births during the same year.
The average interval (T) between HIV infection and detection was estimated by 2 methods. The first method assumes a steady state. In this case, T is calculated by dividing the number (P) of HIV-positive persons a year (y) whose HIV infection was not already known by the number (I) of HIV cases newly detected in the same year.
This calculation also assumes that AIDS mortality is negligible during the period T. This calculation is still valid when the relative change in HIV prevalence during T is small (quasi steady state). T was calculated using equation 1 and the data of the national HIV-AIDS database. The factor P was estimated as the number of pregnant women who test HIV-positive in the year y whose HIV infection was not already recorded by the detection system. The factor I was estimated in the year y by multiplying the annual number of HIV cases detected among women aged 15–49 by the proportion of pregnant women in the same group. These calculations were carried out year by year in the period 1996–2006. A mean and an interquartile range (IQR) were calculated from these values.
When P and I are a function of time (t), P(t) is given by the following equation:
When P(t) and I(T) are a linear function of time, this equation gives T as:
A second estimation of T was obtained using this equation 3 applied to the period 1996–2005 with dP/dt and dI/dt estimated by fitting a linear regression line through the data among pregnant women as described above in the first method. This second estimation is based on derivatives and, thus, has too wide a confidence interval to be indicated.
T0 being the incubation period, the coverage (c) can also be estimated by the following equation:
Each year the detection system finds a fraction of the number of HIV-positive persons not yet detected. This fraction defined the performance (p) of the detection system. This performance was estimated, year by year, by dividing a number (n1) by a number (n2).
Using these values, a mean and an IQR were calculated. In this equation, n1 is the number of HIV-positive women given in the year y by the detection system in the age group 15–49 weighted by the proportion of pregnant women among the women of the same age group in the same year. n2 is the number of HIV-positive women given by the detection system in the year y in the age group 15–49. This estimation is close to reality because all pregnant women are tested for HIV. The value of p calculated using equation 5 assumes that HIV prevalence among women in the age group 15–49 is close to the HIV prevalence among pregnant women of the same age.
We defined the coverage (c) of the detection system at a given time as the percentage of persons living with HIV that were detected before that time. This coverage was estimated in the following way. At the end of a year (y), from the data base we have the total number of cumulated detected HIV cases (H0) and the number of new detections in the same year (Hy). Using the performance of the detection system, we estimated the total accumulated number of HIV infections (Ht) as Ht = H0+Hy/p. The coverage of the detection system is then defined as the ratio H0/Ht.
A mean coverage was calculated using the mean performance. An estimation of the IQR of the coverage was calculated by using the IQR of the performance. To take into account the coverage of the detection system, a corrected value of HIV prevalence for men and women was calculated by dividing by c, given by equation 6, the prevalence given by the data base. We assumed that this coverage is not dependent on gender.
The median (IQR) interval between HIV detection and AIDS was calculated by survival analysis using the dates of HIV detection and the dates of AIDS using data prior to the introduction of ART in 2000.
This study has been approuved by the Ethics Committee of the Instituto de Medicina Tropical "Pedro Kouri", Havana Cuba in its monthly meetting of January 2005.