Singapore has seen a rise in the number of people with Covid-19 entering the country since it reopened its borders to more long-term pass holders on June 19.
The 239 cases who tested positive after coming into the country since then represent almost 30 per cent of all imported cases in the Republic.
Nonetheless, the infections represent only a tiny proportion of people entering the country.
The Ministry of Health (MOH) told The Straits Times that there were more than 83,000 arrivals here by land, sea and air between June 18 and Aug 6 (excluding those arriving by lorry for deliveries). Only 152 imported cases were reported during the same period.
About eight in 10 of those infected had arrived from India and the Philippines - two countries which provide a large proportion of Singapore's foreign workforce, and both of which have suffered a spike in infection rates.
To prevent the infection from spreading in the community, all incoming travellers have to serve a 14-day stay-home notice (SHN), and are tested for the virus before this is over.
The recent rise in imported cases led some ST readers to ask why travellers are not swabbed immediately after they arrive, instead of at the tail end of their 14-day SHN period.
MOH explained that the coronavirus has an average incubation period of five to six days, with a maximum of 14 days.
"A swab test at the point of arrival may not pick up cases during the incubation period," it said.
Notably absent from the list of countries where recent cases were imported from was Malaysia. Some readers had expressed concern about travellers from Singapore's immediate neighbour following news of the special travel arrangements between the two countries.
There have been no imported cases from Malaysia since at least April 27.
Under special travel arrangements such as the periodic commuting arrangement (PCA), travellers from Malaysia undergo a shortened seven-day SHN and a swab test.
Health Minister Gan Kim Yong said earlier this month that the SHN was shortened because Covid-19 prevalence rates in Malaysia are similar to Singapore's or lower.
"Therefore, the risk of infection is quite similar to a fellow Singaporean," he said.
MOH's director of medical services Kenneth Mak had said that most symptomatic visitors display symptoms within five or six days of entering Singapore.
"That allowed us then to think about considering shortening the duration of SHN for countries where the original prevalence (of Covid-19) in that country was low," he said.
Those travelling under the reciprocal green lane (RGL) scheme also need to be swabbed for the virus and must isolate themselves until negative results are returned. They can stay a maximum of 14 days, and must follow a pre-declared control itinerary.
The arrangements allow employers to travel for essential meetings and give workers opportunities to see their families more often.
The cross-border travel arrangements between Singapore and Malaysia kicked off on Monday.
Malaysia's Foreign Minister Hishammuddin Hussein said last month that 2,000 Malaysians and Singaporeans are allowed to cross daily under the PCA.
Under the RGL, 400 Malaysians and Singaporeans can travel to and fro between the two countries a week.