One of the most important observations made in this study was the age difference between neighbourhood cases and distant cases attending public STI clinics in Hong Kong. Our study covered all 6 clinics in Hong Kong which have been providing free drop-in diagnosis and treatment service to anyone who is symptomatic with STI or is concerned about possible infection. It appears that older patients were seen more often in the nearby clinics. This age differential is a cause for concern. The lower mobility of senior citizens could be a reason for the higher concentration of older patients in the vicinity of the clinics. If older patients only go to clinics nearby, then access to STI treatment of those living further away from the clinics is likely to be suboptimal. As treatment offers a window of opportunity for intervention, control of STI spread may also be adversely affected. While the clinics are perceived as conveniently located by younger citizens, our elderly population may have a different view about access. Location of clinics far away from one's residence may be a disincentive for elderly STI patients in seeking treatment. Though STI is a condition of the sexually active, this does not however mean that the infection is confined to young people . Studies have reported a rising incidence of older people with STI . The problem of STI in elderly population can be compounded also by one's low perceived risk of infection, stigma, inconsistent use of condom, and delayed diagnosis .
In this spatial study, two other findings were: firstly, the lower prevalence of syphilis, and secondly a higher prevalence of inconsistent condom use in patients living further off. The higher number of syphilis patients in the vicinity of the STI clinics could be related to the administrative arrangement of referring serologically diagnosed cases to a nearby public STI clinic. Serological screening of syphilis is a common practice adopted by some health services to elderly people with neuropsychiatric diseases and any form of motor or sensory deficit. With the rising age of the population, an increasing number of elderly homes are becoming established. The introduction of health screening would uncover otherwise undiagnosed syphilis. This observation may therefore echo the relatively higher proportion of elderly STI patients in the vicinity of the clinics. Our dataset has not included the reasons for each consultation, which therefore did not allow this possible relationship to be determined. Elsewhere, it has also been reported in the literature that the clustering of STI patients could refer to the clustering of social determinants instead of the infection per se , the relevance of which cannot be substantiated in this study. On the other hand, the marginally higher prevalence of unsafe sexual practice in patients living further from the clinics cannot be explained fully. It can be argued that people living further off may have poorer access to effective safer sex information, or that distant cases represent those with a different demographic profile which may have been associated with the different behavioural pattern. The observations would need to be confirmed by a repeat or expanded study with the objective of determining the association between distance and risk behaviors.
Understandably the spatial variation of STI cases may not necessarily reflect the underlying epidemiologic or behavioural pattern, as it could have been related to the service coverage of individual clinic. It is not surprising to find a higher prevalence of STI in the vicinity of an STI clinic, as patients may be more inclined to present for diagnosis and treatment at a convenient location. Interestingly, our results showed that most of the STI cases did not live near the clinic, even though all clinics are located in residential areas. In some clinics most cases came from a specific distance, implying that they must be residents from another residential area nearby or further away. An inverse relationship between distance and number of cases is not seen. Because of the stigma attached to the disease, some patients may distance themselves from STI services . It is possible that some patients may choose to attend a clinical service unlinked to his/her own residential community. In other patients, they may choose to attend a service near work instead of residence location. It can also be argued that six separate locations cannot provide optimal coverage for STI services, an issue that needs to be further explored when new clinics are planned.
Age differentials aside, our results did not reveal any significant geographic variation in the clinical presentation or diagnoses of STI. This may be related to the pattern of commercial sex industry in the territory. Conventionally, places with discrete foci of commercial sex trade are considered as locations with potential risk of STI spread. In Hong Kong, it is against the law to operate commercial sex trade. While commercial sex workers (CSW) are present, they do not function openly in distinct physical locations . CSW in Hong Kong are apparently quite mobile in their locations of seeking partners and sexual activities. On the other hand, Hong Kong is not just a small area but a place with exceedingly efficient public transport system . Spatial isolation is often not a major issue in term of access to medical facility. It is hard to find STI patients who are geographically isolated because of poor access to public transport. In drawing these and other conclusions on spatial epidemiology, we reckon that the study did carry some limitations. First of all, the analysis was made on patients who have attended the clinic services only during a one-month period in the year 2008. Seasonal patterns, if any, would have distorted the clinical and epidemiologic pictures derived from the study. Secondly, public STI clinics only account for the management of a fraction of all STI cases. Spatial variation of clinical presentations, behaviours and service preference would have been missed if the characteristics of patients not using the Government service differ significantly. As the major service provider using standard protocols for STI management, studies on patients from the clinics do carry an advantage in improving our understanding of STI in the community.