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Thiruvananthapuram, Apr 10: Eight foreign nationals from Italy and United Kingdom, who were undergoing treatment in Kerala, have recovered fully from COVID-19, Chief Minister Pinarayi Vijayan said on Thursday.

The state reported 12 more positive cases of coronavirus on Thursday taking the total number of confirmed cases to 357, Vijayan said as he cautioned that the strict vigil against the pandemic will continue.

While the northern districts of Kannur and Kasaragod reported four cases each, two cases were reported from Malappuram district and one each from Kollam and Thiruvananthapuram districts, Vijayan told reporters after a COVID-19 review meeting here.

Of the eight foreign nationals, seven were undergoing treatment at the Ernakulam Medical College Hospital and one in Thiruvananthapuram Medical College Hospital, Vijayan said, adding that some of the patients were in a serious condition.

The seven foreigners from UK, admitted in Ernakulam medical college, were part of the group which had on March 15 tried to leave the country without permission while being under observation at Munnar, a hill station in the state.

The Italian tourist in Thiruvananthapuram was staying at a resort at Varkala near here and was admitted to hospital on March 13, Vijayan said.

"The recovery of this UK tourist group, which comprised of 83 and 76-year-olds is a testimony to our robust healthcare system and good treatment extended to these patients," the chief minister said.

It has been 100 days since the first COVID-19 case was reported in the state and since then, a total of 357 cases have been confirmed and currently, 258 patients are under treatment in different hospitals.

The current physical distancing guidelines provided by the World Health Organisation (WHO) and by the US Centers for Disease Control and Prevention (CDC) may not be adequate to curb the coronavirus spread, according to a research which says the gas cloud from a cough or sneeze may help virus particles travel up to 8 metres. The research, published in the Journal of the American Medical Association, noted that the the current guidelines issued by the WHO and CDC are based on outdated models from the 1930s of how gas clouds from a cough, sneeze, or exhalation spread.

Study author, MIT associate professor Lydia Bourouiba, warned that droplets of all sizes can travel 23 to 27 feet, or 7-8 metres, carrying the pathogen.

According to Bourouiba, the current guidelines are based on "arbitrary" assumptions of droplet size, "overly simplified", and "may limit the effectiveness of the proposed interventions" against the deadly pandemic.

 She explained that the old guidelines assume droplets to be one of two categories, small or large, taking short-range semi-ballistic trajectories when a person exhales, coughs, or sneezes.

However based on more recent discoveries, the MIT scientist said, sneezes and coughs are made of a puff cloud that carries ambient air, transporting within it clusters of droplets of a wide range of sizes.

Bourouiba warned that this puff cloud, with ambient air entrapped in it, can offer the droplets moisture and warmth that can prevent it from evaporation in the outer environment.

"The locally moist and warm atmosphere within the turbulent gas cloud allows the contained droplets to evade evaporation for much longer than occurs with isolated droplets," she said.

"Under these conditions, the lifetime of a droplet could be considerably extended by a factor of up to 1000, from a fraction of a second to minutes," the researcher explained in the study.

The MIT scientist, who has researched the dynamics of coughs and sneezes for years, added that these droplets settle along the trajectory of a cough or sneeze contaminating surfaces, with their residues staying suspended in the air for hours.

"Even when maximum containment policies were enforced, the rapid international spread of COVID-19 suggests that using arbitrary droplet size cutoffs may not accurately reflect what actually occurs with respiratory emissions, possibly contributing to the ineffectiveness of some procedures used to limit the spread of respiratory disease," Bourouiba wrote in the study