In Hong Kong, about 56% of the physicians work in the private sector. The private system provides 20% of the inpatient medical care, 11% of hospital beds, and 70% of the outpatient visits. Patients generally seek private outpatient medical care by self-referral. Medical fees are usually paid at the time of service, with less than 10% of fees being paid directly by insurance companies. Three types of private practitioners participated in the study: general practitioners (GP), obstetric and gynaecology (O&G) doctors and dermatologists and venereology (D&V) doctors. The majority of the local patients seeking consultation for STDs from private doctors would be seen by such private doctors[15, 16]. A previous study which was commissioned by the Department of Health in Hong Kong in June 2007 requested the aforementioned types of private doctors and public doctors to record information of all patients presenting with STD symptoms within a specific period of 15 days. In that study, the sampling frame of the private doctors included all members of the Hong Kong Association of Specialists in Dermatology and all O&G and GP doctors whose valid contact information was listed in the websites of the Medical Council of Hong Kong http://www.mchk.org.hk/doctor/index.htm, the Yellow Pages http://www.yp.com.hk/home/en/html/main/home.aspx and The Hong Kong Doctors Homepage http://www.hkdoctors.org of the Hong Kong Medical Association. Some research assistants then verified the validity of the contact information by phone or by mail. A total of 277 private doctors (247 GPs, 14 O&G doctors and 16 D&V doctors) participated in the 2007 study (representing 9.3%, 7.9% and 30.2% of all doctors with valid contact information) and all of them were invited to participate in the present study.
There are a total of eight Social Hygiene Clinics (SHC) in Hong Kong which are responsible for the prevention and control of STDs. SHC provide walk-in service for consultation, counselling and medical treatment for patients with STDs. Staff of the SHC carry out contact tracing, health education and outreach activities to control the spread of STDs. In collaboration with the Department of Health, all doctors in five major SHC, out of the eight clinics, participated in the present study.
An invitation package which included a self-explanatory introduction letter, a sample log-form and a reply slip was sent to each of the aforementioned 277 doctors from November to December 2008. All prospective participants were requested to fill out the reply slip and return it to the research team by fax or mail. About one week after the invitation letter was sent, a follow-up telephone call was made to all prospective participants by a team of experienced interviewers to confirm their participation status. With respect to unanswered calls, at least four other independent calls were made on different hours in different days before the contact number was considered as an invalid one.
A study kit, which contained an instruction manual, a set of log forms and a reminder sheet, was delivered to the participants' clinic by a research assistant one week prior to the commencement of the data collection time period. The instruction manual introduced the objective of the study and the data collection procedure in detail to the doctors. Doctors in the SHS clinics received training on how to fill out the log-form. An enquiry hot-line was also launched during the study period. The anonymous log-form was designed by the research team to record the number of patients seen by the doctor on a particular day and the number of adult patients (aged 18 or above) presenting with genital warts to the doctor. The patients' names or other personal identifiable information were not collected. Genital warts were defined as clinical features of warts in or around anogenital area which include internal/external genitalia, perineum and perianal region. Diagnosis of genital warts is primarily based on clinical judgments and no laboratory tests were required. The patients with genital warts were asked whether he/she had ever noted similar symptoms before or been diagnosed with genital warts previously in any health care facilities. The cases with no past symptoms or clinical diagnosis of genital warts were defined as new cases. Demographic information such as gender and year of birth of the genital wart cases was recorded.
During the 14-day data collection period (January 5 to January 18, 2009), all participating doctors were required to fill out the log-form on a daily basis and fax it back to the research office. If the log-form was not received from a particular clinic on time, reminder calls were made by the research team to ensure the completeness of data. Long sensitive questionnaires were avoided in order to ensure the data accuracy. Research assistants cross-checked every form on a daily basis and contacted the doctor involved in the case of any unclear entries. The completed log forms were sent to the research team at the end of the data collection period for verification. As an incentive, a supermarket coupon (HK$200 or about US$25) was sent to participating doctors who completed the study. Ethics approval was obtained from the Chinese University of Hong Kong.
The total number of patients presenting with genital warts to local private doctors during the data collection period was projected using the stratification sampling method[19, 20]. GPs were stratified in 18 strata according to the district-board classification system. Hence, there were a total of 20 strata (18 GP strata + 1 O&G doctor stratum + 1 D&V doctor stratum) for private doctors. The total numbers of GPs in each of the 18 districts and the number of D&V and O&G were obtained from the Department of Health. The projected number of patients in a stratum is hence:
N: projected number of patients in the stratum
N': Observed number of patients in the stratum
The territory-wide number of patients presenting with genital warts to private doctors during the study period was estimated by summing up the figures projected for all the 20 strata.
The number of adult genital warts patients seen by doctors of the five SHC during the study period was used to project the total number of adult patients seen by doctors of all eight SHC in the territory, according to the distribution of the number of genital warts cases presented in the eight individual clinics identified from a previous STD surveillance study conducted in 2007. Such data were obtained from the local Department of Health. An important assumption was made that the number of genital warts patients seen by the participating doctors was representative of those seen by all doctors territory-wide.
The total number of new adult genital warts cases in Hong Kong presenting with symptoms to local private and public doctors during the study period was obtained by summing up the projected number of patients seen by private and public doctors. Bootstrap methods were used to estimate the respective 95% confidence intervals. The intervals were calculated using Matlab V7.1 (the MathWorks, Inc.), based on a reasonably large number of 30000 bootstrap replications.
The incidence of genital warts was estimated using the total projected number of new genital warts cases detected by public and/or private doctors in Hong Kong during the study period, divided by the person-year exposure of the Hong Kong adult population age 18 and above during the same time period. According to the 2006 census, the sizes of the local male, female and total adult population age 18 and above years old were respectively 2,650,340, 3,006,691 and 5,657,031. The person-year exposure to the risk of developing new genital warts during the study period hence equals to the adult population size multiplied by 14/365.