This is the latest population-based study that investigates the incidence and prevalence of gout in Hong Kong. Subjects included in this study are representative of the general population. We reported an increase in the incidence and prevalence of gout in Hong Kong. Ageing population is definitely one of the contributing factors. The number of Hong Kong people aged ≥ 65 years increased from 865,200 (12.5%) in 2006 to 1,192,700 (16.1%) in 2015 . As population ageing continues, we expected the crude incidence and prevalence of gout will further increase.
Our study also showed a non-linear increase in age-specific incidence and prevalence of gout. This phenomenon was also shown in a population-based study in Taiwan . The incidence of gout was highest at the age ≥ 80 because this age group had the highest number of incident cases but the lowest PY.
The latest incidence and prevalence of gout in Hong Kong were similar to those in the western countries, including the UK [2, 15], New Zealand , Denmark , Australia , and the US according to the US National Health Nutrition and Examination Survey in 2015–2016 . However, the prevalence of gout did not increase in the US.
An increase in both the age- and sex-adjusted incidence and prevalence suggested that other risk factors, including alcohol consumption, obesity, and diabetes, might contribute to this observation. The Population Health Survey showed that the proportion of Hong Kong people with overweight or obesity increased from 38.8% in 2003/2004 to 50.0% in 2014/2015 [14, 19]. Results of this survey also showed that there was an increase in regular alcohol consumption. The proportion of population with regular alcohol consumption increased from 9.5% in 2003/2004 to 11.1% in 2013/2014, while the prevalence of self-reported diabetes increased from 3.8 to 5.5%. Although CDARS does not capture body mass index and alcohol consumption, results of this survey may explain the increase in the incidence and prevalence of gout beyond population ageing.
The management of gout remained suboptimal in Hong Kong because the utilisation of ULT was insufficient . The prescription of febuxostat was less than 1% because it was not subsidised by the government. Although allopurinol was fully subsidised, only 24.5% of patients with gout received this medication .
The efficacy of ULT in reducing serum urate levels has been demonstrated in many randomised controlled trials. In addition, the use of xanthine oxidase inhibitors in patients with gout is associated with cardiovascular and renal benefits. Epidemiological studies suggested that allopurinol might decrease mortality in patients with congestive heart failure and the risk of myocardial infarction . However, allopurinol is associated with an increased risk of severe cutaneous adverse reaction in patients carrying the HLA-B*5801 allele. According to a population-based study conducted in Taiwan, among Han Chinese who carry the HLA-B*5801 allele are 580 times more likely to develop allopurinol-induced severe cutaneous adverse reaction than those who do not carry the allele . Although febuxostat is more effective than allopurinol, it is associated with increased cardiovascular and all-cause mortality compared to allopurinol . It is worth noting that the results have been criticised due to high drop-out and many other methodological issues. Nevertheless, many studies have confirmed that hyperuricaemia is associated with increased mortality, and therefore, ULT should be considered seriously in patients with gout.
This study is not without limitations. We used the diagnosis codes in CDARS; therefore, the diagnostic accuracy depends on physician’s coding. Compliance to ULT cannot be captured in CDARS. Therefore, the effect of compliance to ULT on serum urate levels among patients with gout cannot be assessed in this study. In addition, not all patients with gout had a serum urate level measurement. Therefore, the mean serum urate levels cannot represent all the patients with gout in this study. Although we covered more than 90% of the general population in Hong Kong, CDARS does not include patients receiving medical care in the private sector. This social bias could not be remedied as socio-economic data are not included in the database.