HIV/AIDS Epidemiology in Hong Kong - 2006
(Adopted from HIV Surveillance Report -2006 Update.)
The Department of Health has implemented a voluntary anonymous HIV/AIDS reporting system since 1985. The system received reports from doctors and laboratories. Medical doctors report newly diagnosed positive cases by a standard form (DH2293). In the past, only cases with Western Blot confirmed HIV antibody positive laboratory result were counted as HIV infection for cases aged above 18 months. Since the 4th quarter of 2006, cases with a PCR positive result and clinical or laboratory indication of recent infections were also counted as HIV infection in the reporting system, in view of the increasing regular detection of such cases.
In 2006, the department received 373 HIV reported cases and 73 AIDS reports, which increased 19% in HIV cases and 14% in AIDS cases as compared with 2005. It made the cumulative totals reached 3198 and 855 for HIV and AIDS reports respectively. Two cases of PCR positive with clinical or laboratory indication of recent infections were included as HIV infection under the revised definition this year. Public hospitals/clinics/laboratories were still the commonest source of HIV reports in 2006, which accounted for over half of the reports. Private hospitals/clinics/laboratories were another common source of HIV reports (20.9%). Notably, the AIDS service organisations played a more significant role in HIV reporting in 2006 (4.6%). The number of reports from other sources has remained stable.
Eighty percent of reported HIV cases were male. The male-to-female ratio remained at 4.5:1 in 2006. About 60% of reported cases were Chinese. Asian accounted for nearly one fifth of reports. The median age of reported HIV cases was 34. The age specific rate of sexually acquired infections rose in men, especially in the age group 20-24 and 25-29. Over 60% of reported cases were believed to acquire the virus through sexual transmission in 2006. Injecting drug use accounted for 15% of HIV infections in 2006. There were two reports of HIV transmission through perinatal contact in 2006. The suspected routes of transmission were not reported in about a quarter of cases. This means that sexual transmission has accounted for nearly 80% of HIV reports with defined risks.
Sexual contact was the commonest route of HIV transmission in Hong Kong. Both heterosexual and homosexual/bisexual contacts were important risk factors. In 1980s and early 1990s, the early years of AIDS epidemic in Hong Kong, it used to report more cases from men who have sex with men, including both homosexual and bisexual contacts. The trend then reversed with more heterosexual transmission reported since 1993. A rising trend in MSM has been observed since 2004. The situation was worsening this year. The number of MSM cases increased from 96 cases in 2005 to 112 cases in 2006, showing a 17% increase. At the same time, the number of heterosexual male cases remains at a stable level (71 in 2005 and 74 in 2006).
Nearly 40% of male HIV reports this year contracted the virus through homosexual or bisexual contact. Heterosexual contact in male cases accounted for about 25%, whereas the routes of transmission were not reported in the rest 25% male cases. The ratio of heterosexual men against MSM dropped from its peak of 4.1:1 in 1998 to 0.7:1 in 2006. (Box 1.1) That meant more men were infected through homosexual/bisexual contact than heterosexual contact for consecutive two years, which was a reverse of the situation in earlier years.
Box 1.1 The number of MSM cases is taking over heterosexual men cases in the reporting system again.
The major attributes of the rise in MSM were Chinese and of age group 20-39. Nearly 90% of MSM cases in 2006 were Chinese. Caucasians accounted for only 5%. A rising trend in the number of reported Chinese MSM cases was observed in recent years. (Box 1.2) The median age of MSM cases at report was 34, as compared to 39 of heterosexual man cases. Age group 30-39 was the commonest age of reporting in MSM, which accounted for 37% in 2006. The HIV infected MSM population was getting younger. The median age dropped from 37 in 2005 to 34 in 2006. (Box 1.3) Although the rising trend in the age group of sexual active, 20-49, was observed, a prominent increase in the absolute number of cases was observed in the group 20-29. The number of cases in 20-29 doubled as compared with last year. More cases were reported below the age of 20 too. (Box 1.4)
Box 1.2 Ethnicity Breakdown of HIV-infected MSM cases (1984-2006)
Box 1.3 Median age of HIV-infected MSM cases, heterosexual man and heterosexual women (1984-2006)
Box 1.4 Age breakdown of HIV-infected MSM cases (1984 - 2006)
No systematic data on local MSM HIV prevalence was available previously. AIDS Concern's voluntary HIV testing service targeting MSM showed a rising trend in test positivity in recent years. (Box 1.5) This year a community based survey (PRiSM) was conducted in 20 gay saunas, bars and clubs. A total of 859 urine samples were collected and the survey revealed a HIV prevalence of 4.05% among MSM attending these venues. Although MSM in internet and those not attending these venues were not covered, the prevalence was several times higher than that of other at risk populations in Hong Kong.
Box 1.5 HIV seroprevalence in AIDS Concern's voluntary HIV testing service
| Year | No. of blood samples | No. of samples tested anti-HIV+ | Prevalence (%) | 95% C.I. for prevalence (%) |
| 2000 | 38 | 0 | 0 | (0.000 - 0.000) |
| 2001 | 107 | 1 | 0.93 | (0.024 - 5.207) |
| 2002 | 130 | 1 | 0.77 | (0.019 - 4.286) |
| 2003 | 223 | 2 | 0.90 | (0.109 - 3.240) |
| 2004 | 332 | 6 | 1.81 | (0.663 - 3.934) |
| 2005 | 483 | 12 | 2.48 | (1.284 - 4.340) |
| 2006 | 610 | 10 | 1.64 | (0.786 - 3.015) |
The condom use rate of MSM attending AIDS Counselling and Testing Service remained static for both regular partners and casual partners in recent years. Similar trend was observed among those attending AIDS Concern's testing service. The PRiSM survey revealed that 73% of MSM consistently used a condom in anal sex with casual sex partner but only 41% consistently used a condom with regular sex partner during anal sex.
The number of heterosexual cases remained stable in 2006. Totally 114 cases was reported, as compared with 110 cases in 2005. Because of increasing number of reported cases in other routes of transmission, the proportion accounted by heterosexual contact decreased from 35% in 2005 to 30.5% in 2006. The male to female ratio for heterosexual cases was 1.9:1. The median age of heterosexual cases in 2006 was 38. Heterosexual male cases were mainly (77% in year 2006) Chinese whereas Chinese only accounted for half (55% in year 2006) of female cases.
A majority of Social Hygiene Clinics attendees reported unprotected heterosexual contact. The seroprevalence of Social Hygiene Clinic attendees remained stable at around 0.1% (0.13% in 2006). On the other hand, the trend of sexually transmitted infections (STI) provides information for the understanding of risk of HIV infection in the community. Although it was estimated that Social Hygiene Clinics took care of only 20% of STI cases in the territory, it was still a very important sentinel site. There was a slight decrease in the total number of STI cases in Social Hygiene Clinics, an aggregate of 16588 in 2006 as compared with 18435 cases in 2005. A 10% decrease was observed in all the common STI diagnosis. The decrease of cases was more obvious in gonorrhoea, from 1748 cases in 2005 to 1595 cases in 2006.
A territory wide community based HIV seroprevalence and behavioural survey in female sex workers (CRiSP) were conducted this year with the participation of five non-governmental organisations serving female sex workers. The survey collected 996 eligible urine samples from different districts and settings. It revealed a prevalence of 0.19%, which was similar to that of social hygiene clinics attendees.
The condom use rate with commercial partners remained steadily high among adult heterosexual men attending Social Hygiene Clinics and AIDS Counselling and Testing Service. The level was over 80% among those attending AIDS Counselling and Testing Service. In the CRiSP survey, a high condom use level was revealed among female sex workers in Hong Kong too. The consistent condom use rate for vaginal sex with customers among respondents was 92%.
In 2006, the reporting system recorded 56 cases of HIV transmission through injecting drug use. The number was similar to that of 2005, but at a higher level as compared with several years ago. Most of the cases were Asian, non-Chinese. The median age was 28.5. About 10% of injecting drug user cases was reported from methadone clinics.
It was estimated that over 70% of heroin users attended methadone clinics at any one time. The Universal HIV Antibody (Urine) Testing Programme replaced the unlinked anonymous screening (UAS) in methadone clinic as the seroprevalence study in 2004. 7911 urine samples were collected in the programme in 2006 with a coverage rate of 90%. The coverage of the programme was similar to that of 2005. The programme tested 12 positive cases in 2006 and with the 16 previously known positive cases still attending methadone clinics, totally there were 28 HIV positive drug users attending methadone clinic this year. The seroprevalence over the year, including the UAS period, was stable at below 1%. The seroprevalence of methadone clinic attendees in 2006 was 0.362%, which was not significantly higher than previous years.
Although a significant proportion of drug users were injectors, various surveys revealed that the proportion of needle sharing was relatively low. The trend remained stable over the years.
In 2006, no reported case was linked to infusion of blood or blood product. Actually no HIV infection from local contaminated blood or blood product was found in the recent several years. The seroprevalence of new blood donors at Hong Kong Red Cross Blood Transfusion Service was at a low level of around 0.003% in 2006.
In 2006, two perinatal HIV infections were reported. There were scattered cases reported across the years and some cases were retrospective reports. The Universal Antenatal HIV Testing was implemented in September 2001. About 40,000 pregnant women attending public antenatal services were tested every year and the coverage of the programme reached 98% in 2006 and revealed the seroprevalence of HIV infection in pregnant women to be 0.02%, which is similar to that of previous years. Eight pregnant women were tested positive in the programme this year. Two women terminated their pregnancy and two women delivered their babies by Caesarean Section. The rest gave birth by vaginal delivery.
The information of voluntary reporting was becoming incomplete as there are an increasing proportion of cases reported without a risk factor. Similar to last year, over a quarter of cases reported without a suspected route of transmission. This was especially so for cases without clinical reporting. Undetermined risk is commoner in cases reported by private hospitals/clinics/laboratories. While it is understandable that the route of transmission may not be determined in every single case, every effort should be made to report this crucial information so that meaningful aggregate data could be generated for a better understanding of local HIV epidemiology in Hong Kong.
The annual number of reported AIDS cases was dropping since 1997, the year of introducing highly active antiretroviral therapy (HAART) in Hong Kong but the trend halted. Seventy-three AIDS cases were reported as compared with 64 cases in 2005. 61 cases (83.6%) of the AIDS reports this year has their AIDS reported within 3 months of HIV reporting.
The primary AIDS defining illness (ADI) pattern of the reported cases also changed slightly in recent years. Pneumocystic jirovechi pneumonia (previously named Pneumocystic carinii) has been the commonest ADI in Hong Kong. This year, Pneumocystis pneumonia and Mycobacterium tuberculosis were similarly common among AIDS cases this year. They accounted for 27 cases (36.9%) and 26 cases (35.6%) as primary AIDS defining illness respectively. They were followed by Penicilliosis (11, 15.1%), and other fungal infections (4, 5.5%). On the other hand, unlinked anonymous testing in tuberculosis patients demonstrated a seroprevalence of 0.357% in 2006. An increasing trend was showed and stayed at a relatively high level since 2002. This figure was even higher than that of Methadone Clinic attendees and Social Hygiene Clinic attendees.
The median CD4 of newly reported HIV cases in 2006 was 216.5. Reporting of CD4 level is becoming a routine practice in physician. It provides useful information on the timing of diagnosis in the course of HIV infection. 61.7% of HIV cases in 2006 reported the CD4 level at diagnosis. The median CD4 for those aged less than 55 has been stable at around 200 (196 - 258.5) for the past 5 years. One the other hand, there was a continued decreasing trend in median CD4 count among those who are aged 55 and above. It suggested that more patients reported at age 55 or above were diagnosed at a late disease stage. (Box 1.6 & 1.7)
Box 1.6 - Reported CD4 levels at HIV diagnosis
| Year | No. of HIV reports | No. of CD4 reports (%) |
Median CD4 (cell/ul) | CD4>=200 (cell/ul) (%) |
||
| 2001 | 213 | 162 | ( 76.1% ) | 233.5 | 85 | ( 52.5% ) |
| 2002 | 260 | 201 | ( 77.3% ) | 197 | 100 | ( 49.8% ) |
| 2003 | 229 | 166 | ( 72.5% ) | 205 | 85 | ( 51.2% ) |
| 2004 | 268 | 177 | ( 66.0% ) | 215 | 95 | ( 53.7% ) |
| 2005 | 313 | 210 | ( 67.1% ) | 199.5 | 105 | ( 50.0% ) |
| 2006 | 373 | 230 | ( 61.7% ) | 216.5 | 122 | ( 53.0% ) |
Box 1.7 - CD4 Reports by age group
| Age | Year | No. of HIV reports | No. of CD4 reports (%) |
Median CD4 (cell/ul) | % of CD4 >= 200 (cell/ul) | |
| <55 | 2001 | 190 | 146 | ( 77% ) | 258.5 | 54% |
| 2002 | 230 | 183 | ( 80% ) | 196 | 50% | |
| 2003 | 190 | 139 | ( 73% ) | 228 | 53% | |
| 2004 | 225 | 156 | ( 69% ) | 226.5 | 56% | |
| 2005 | 280 | 187 | ( 67% ) | 198 | 50% | |
| 2006 | 339 | 209 | ( 62% ) | 237 | 56% | |
| >=55 | 2001 | 22 | 16 | ( 73% ) | 96 | 38% |
| 2002 | 24 | 18 | ( 75% ) | 212.5 | 50% | |
| 2003 | 32 | 27 | ( 84% ) | 108 | 44% | |
| 2004 | 32 | 21 | ( 66% ) | 82 | 33% | |
| 2005 | 29 | 23 | ( 79% ) | 223 | 52% | |
| 2006 | 28 | 21 | ( 75% ) | 145 | 24% | |
In 2006, about 80% of HIV reports had their subtypes documented. CRF01_AE and Subtype B of HIV-1 strains were the most common subtypes identified in Hong Kong. They together accounted for 69% of all HIV cases. CRF_01AE was found to be commoner in female, Asians non-Chinese, heterosexuals and IDU. The subtype B was commoner in Caucasian, MSM and C subtypes in females, Asians and sexually transmitted cases. An increasing diversity of subtypes and its circulating recombinant forms was also noted. (Box 1.8)
Box 1.8 - HIV Subtypes in Hong Kong
| 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | |||||||
| Annual HIV Reports | 213 | 260 | 229 | 268 | 313 | 373 | ||||||
| No of reports with subtypes (%) | 90 | (42%) | 228 | (88%) | 204 | (89%) | 202 | (75%) | 258 | (82%) | 293 | (79%) |
| Subtype (%) | ||||||||||||
| CRF01_AE | 56 | (26%) | 122 | (47%) | 99 | (43%) | 95 | (35%) | 125 | (40%) | 139 | (37%) |
| B | 24 | (11%) | 78 | (30%) | 60 | (26%) | 71 | (26%) | 101 | (32%) | 114 | (31%) |
| CRF008_BC | 0 | (0%) | 1 | (<1%) | 4 | (2%) | 10 | (4%) | 6 | (2%) | 11 | (3%) |
| C | 5 | (2%) | 15 | (6%) | 21 | (9%) | 3 | (1%) | 2 | (1%) | 6 | (2%) |
| Others | 5 | (2%) | 12 | (5%) | 20 | (9%) | 23 | (9%) | 24 | (8%) | 23 | (6%) |
A cluster of HIV-1 Subtype B infections with similar gene sequencing was first detected in 2005. Upon testing of newly reported and prior blood samples, the cluster expanded from 20 cases to 42 cases this year. Those newly added cases were reported within year 2006. The 42 cases were all male and belonged to the age range 22-54 years. Risk factors for HIV infection were reported as unprotected homosexual/bisexual contact in 33 cases (78%).
Two more clusters of HIV-1 Subtype B infection were detected in 2006. The first one involved 12 men aged between 34 and 67. Homosexual/bisexual contact was accounted for 83% of cases as route of transmission. The second one involved seven men aged between 22 and 33. All cases of these two clusters reported homosexual or bisexual contact as suspected route of transmission.
The number of HIV reports was persistently on a rise in 2006. The annual HIV reports used to be around 250. The total number of HIV reports in 2006 was 373, which was a 19% increase as compared to 2005. In the previous five years, there was 15-20% increase in HIV reports every year except in 2003, when SARS outbreak occurred. The rise this year was mainly contributed by increasing reports from Men who have Sex with Men. An increase in injecting drug users was observed but mainly in non-Chinese population, which suggested non-local infections.
The number of HIV reports among MSM continued to rise and it accounted for even a larger proportion this year. The HIV situation in MSM was really worrisome because the increasing trend has persisted. The first community-based seroprevalence survey revealed a high prevalence suggested that the increasing number of reports could not solely be explained improved awareness in MSM or increased number of testing. Both condom usage rates of MSM with casual and regular partners remained at a lower level than that of heterosexual men visiting sex workers.
The expansion of the cluster with similar gene sequencing which detected last year and detection of two more clusters further supported an increased risk of HIV transmission among MSM in Hong Kong. These clusters suggested that the HIV transmission among MSM were taking place locally. This was echoed by data on the suspected places of infection in HIV reports that about 70% MSM cases believed they contracted the virus in Hong Kong. In contrast, only about 40% of heterosexual men believed they contracted the virus locally. These data, including higher HIV prevalence, lower condom use rate, occurrence of clusters, pointed to that the local HIV epidemic in MSM would persist.
HIV transmission in heterosexually acquired infections appears to be similar to the past with no obvious rise. The number of reports for heterosexual contacts remained stable over the years. A significant proportion of non Chinese cases suggested infections outside Hong Kong. Even for heterosexual men, only 40% of their contacts were believed to have occurred in Hong Kong. The prevalence in social hygiene clinics attendees, female sex workers and antenatal women were all below 1%. The condom use rates of commercial sex were high on both sex worker and client side.
Although the number of HIV-infected injecting drug users was persistent at a high level, an escalating growth of HIV infections in injecting drug users was not expected at present. Same as last year, most reported injecting drug users were Asian non-Chinese. It was believed that those non-Chinese acquired the infection outside Hong Kong. The number of HIV infections in drug users contributed by the local infections was not largely different from previous years.
Several massive universal testing programmes were implemented over the years and played an important role in the surveillance system. Two community-based integrated surveys were new initiatives this year. These surveys filled the important knowledge gap in men who have sex with men and female sex workers and opened a new page for the HIV surveillance in Hong Kong. Although the generalisability of their results could be questioned, these surveys tried to adopt a structured sampling strategy and the results provided information we never had before. The trend of seroprevalences and behavioural indicators would still provide invaluable information for HIV prevention.
