For the past two years, once-mundane aspects of everyday life in Hong Kong have been rendered virtually impossible without first scanning QR codes into the officially mandated “Leave Home Safe” app. Now finally scrapped, along with most other precautionary measures deemed essential merely a few weeks ago, that this surveillance mechanism provided limited overall effectiveness in the face of sudden surges seems a fair observation. As soon as Omicron arrived in Hong Kong, late in 2021, official complacency, tragically combined with rock-bottom levels of public trust towards virtually any pronouncements made by those who ruled over them, inevitably saw Covid-19 case numbers mushroom exponentially. Related deaths among the elderly, vulnerable and unvaccinated soared to the world’s highest levels per head of population over the following months. One hopes that valuable lessons for future public health emergencies have been learned the hard way by those in authority. Confronted with this rapid onslaught, Leave Home Safe’s much-vaunted contact tracing ability collapsed, and it was soon viewed by many residents as simply one more vexatious nuisance to navigate in their everyday lives. Forms of contact tracing are not new in Hong Kong. Evidence from the past suggests that technically straightforward measures, when combined with high levels of trust among those the measures were aimed towards, offered significant opportunities for controlling disease. You can’t fault Hongkongers’ ingenuity, but logic isn’t their strong suit More than a century ago, a surprisingly effective, pre-digital-era method was devised to protect the sexual health of members of the British garrison stationed in Hong Kong. Most younger servicemen during that era were single, and not usually by choice. With low pay, general conditions of overseas service and lack of available marriage partners, most soldiers had no opportunity for any regular sexual life without periodic recourse to prostitutes. No moral judgment resides in this observation; brothel visits were simply an everyday fact of military life, which was realistically – if hypocritically – accepted and acknowledged by all concerned. Frequent recourse to sex workers, however, led to an exponentially increased risk of venereal disease. Before the discovery of Salvarsan (the first effective cure for syphilis) in 1910 and the development of early antibiotics throughout the 1930s, few reliable treatments existed. Syphilis was incurable and invariably fatal in the longer term. Gonorrhoea could be ameliorated by various treatments, but permanent remission was uncertain. Acquisition of venereal disease was officially regarded as a self-inflicted injury; an infected serviceman would be punished for having exposed himself to the risk – reduction in rank, and consequent loss of pay, were usual penalties. How Hong Kong’s unattached British servicemen found love between the wars Mitigation measures based upon contact tracing were initiated, and detailed, effective protocols developed. Known brothels, with the cooperation of the owner, were designated as “in bounds” for members of the armed forces to visit. Prostitutes working there were given regular free, comprehensive medical examinations by garrison medical officers to certify that they had no venereal or other disease, such as tuberculosis. All prostitutes working within those brothels were required to have an up-to-date health passbook, which listed their name and other details, and the countersigned and chopped date of their last medical check-up. Individual patrons had to list their own information, which included the date and time of their most recent visit, in the same passbook. Infection chains could thus be swiftly curtailed upon detection, and identified prostitutes given medical treatment, and not permitted to work, until cured. Pseudonyms were humorously deployed; a serviceman might sign in as Benito Mussolini or Lloyd George, and enjoy the company of Mae West or Minnie Mouse but nevertheless, close contacts could be traced when real names were later disclosed if an infection occurred. If a soldier followed the stated guidelines, went to a designated brothel, and selected a sex worker with an up-to-date medical document, then he could not reasonably be held responsible should he catch something.