Emotions are bound to run high with the surfacing of Hong Kong’s first locally transmitted Covid-19 cases in 23 days. The 66-year-old woman and her granddaughter had not recently travelled outside the city, and there is a scramble to identify the source and track down and screen people they had been in contact with. Some social-distancing restrictions were relaxed last Friday and will expire next week, so questions are now being raised whether they should be reviewed. Those are decisions authorities have to make after a thorough investigation and consideration of the facts, but the advice of disease experts that wider community testing is necessary needs attention. Relatives of the pair who were in close contact have either been taken to hospital or quarantined. Testing of others who were in proximity is under way as is a search for those who could have been exposed to them. As proof of the concern, tests of residents of the two buildings involved in the cases in Tsuen Wan will be carried out. An investigation will hopefully determine how human-to-human transmission of the disease occurred. The new cases have also prompted the government to step up testing. From Friday, airport workers – determined to be most at risk of coming into contact with imported cases – will be included, and plans have been announced to extend it to psychiatric patients and homes for the elderly and disabled. But coronavirus disease experts contend that isolated testing does not go far enough in revealing the true extent of Covid-19 in the community; those who are carriers, but show only mild symptoms or none at all, could still pass it on. Such a possibility is why the emergence of fresh clusters of infections of Covid-19 on the mainland have caused alarm. As with Hong Kong, Covid-19 was considered sufficiently under control in many parts of the country and restrictions had been eased to enable a gradual resumption of economic activity. Hundreds of Hong Kong households to be screened amid cluster fears But cases in Wuhan, the central city where the disease first emerged, have prompted officials to order the retesting of more than 14 million people, including migrant workers, and travel limits have been reimposed in Jilin, the second-biggest city in the northeastern province of the same name. South Korea has similarly had to rethink its strategy after dozens of infections linked to clubs in an entertainment district in Seoul. Hong Kong’s strategy for dealing with Covid-19 has won international praise and the low number of deaths and local cases amply proves the effectiveness. Mask-wearing, cleanliness, social distancing, vigilance, contact tracing and quarantining have been the hallmarks of success. They have been highly effective and have to be maintained given the outside threat. But efforts should be made to widen testing, whether randomly or in a more targeted way. Help us understand what you are interested in so that we can improve SCMP and provide a better experience for you. We would like to invite you to take this five-minute survey on how you engage with SCMP and the news.