【明報專訊】The fourth wave of COVID-19 infections has broken out on construction sites repeatedly, and the third runway cluster at the airport has become the latest focus. The risk of cross-infection on construction sites is high because workers come and go frequently, many of them are odd-jobbers, and there are a high number of people accessing the sites. It is easy for the virus to spread when someone is infected. The recent outbreaks in old districts can be traced back to construction site clusters. The government has been sealing off buildings where an outbreak has occurred and conducting mandatory testing there. That, however, mainly targets the lower reaches of the chain of transmission. As the upper reaches are not targeted, it is difficult to eliminate the virus at source. The repeated outbreaks on large-scale government construction sites, one of which has even seen one outbreak after another, imply that there must be a major loophole in anti-pandemic efforts. The role of the Development Bureau and other relevant departments should be reviewed. Construction workers have a hand-to-mouth existence. Property developers are worried that delays in the completion of construction projects will cost them money. It is inevitable that they do not want construction to be suspended. If the authorities, for the sake of "meeting the deadlines for infrastructural projects", handle anti-pandemic work in a haphazard manner, it will be difficult to close these loopholes effectively. The government should require construction site workers to undergo mandatory testing regularly. If more than one person is infected, work must be suspended for 14 days.