Sexually transmitted infections emerge from a recent epidemiological study as a particularly pressing concern for Chinese public health at the present time.  Yang & Li (Y&L) assess trends in incidence and mortality in 45 notifiable infectious diseases across China over the decade since the SARS tragedy in 2003 brought important changes in Chinese public health strategies (2003-2013). The main interest of the authors is to investigate the effectiveness of the new strategies.  But, for readers of this journal, what will be especially interesting about this study is the unique profile of three sexually transmitted – or potentially sexually transmitted – diseases: syphilis, HCV and HIV.

In terms of current incidence these three occupy 6^th, 8^th, and 15^th place among the 45, with yearly incidence per 100,000 of, respectively, 20.75, 9.33, and 3.11.  In respect to mortality, HIV far outstrips all the others (even TB), with 48,199 deaths over the ten year period.  However, syphilis, HCV and HIV differ from other high-incidence diseases – hepatitis B, TB, mumps and bacterial dysentery (respectively, 2^nd to 5^th in the incidence table) – in that their year-on-year incidence is increasing, and at an impressive rate (estimated at a yearly 16.3%, 19.2% and 16.3% averaged over the decade).  These increases are unparalled except in the case of hand, foot and mouth.  The trend in STI incidence emerges particularly strongly against the background of overall trends in the other notifiable diseases. These have, on the whole, been towards stabilization in the latter half of the decade (2009-2013), following an earlier rise likely due in part to technological progress in laboratory detection and case identification (2003-2009).

This raises the questions whether, in the case of STIs, there are particular social factors at work.

For the authors of the study, syphilis, HCV and HIV fall into the category of those diseases whose recent spread can be attributed to the enormous demographic upheavals that have brought over 10% of the population from poor rural areas to the big urban centres in search of economic opportunities, and to ‘augmented human connectivity’.  As regards population mobility, the opinion of Y&L is corroborated by Chen & Tucker (STIs), and – in the case of MSM populations – by Yu & Shang (STIs).  Interestingly, Y&S identify a class of ‘recent migrants’ to the big cities, whose risk profile appears to differ very considerably from that of longer-term residents. Young FSM – many of them also recent migrants to urban centres – appear to represent another high-risk group (Zhang & Luchters (STIs)).  As for the related factor of ‘augmented human connectivity’, this has also been strongly corroborated (Tang & Tucker (STIs)).  Other studies, however, have traced regional outbreaks in these infections – syphilis, HCV and HIV – to causes that are less obviously linked to recent demographic change.  Zhang & Tang (STIs), for example, emphasize the part played in Guangxi by female sex workers who are patronized by older rural workers.  Epidemiological factors, especially over such a vast area, will obviously be complex and multifactorial.