On Wednesday, the 56-year-old scientist from the Agency for Science, Technology and Research (A*Star), who works at Biopolis, denied that he had done all that despite having symptoms.

He insisted that he had monitored his health and acted responsibly by calling the H1N1 hotline, 993, as soon as he found that he had a fever on Monday.

The ministry had said on Tuesday that a number of recent H1N1 patients had gone to work, shopped or attended mass activities before they found out they were ill. That was making it hard to trace others who might be at risk, and also heightened the possibility of the illness spreading in the community, it said.

In an e-mail sent through A*Star to The Straits Times on Wednesday, the researcher said he did not develop any flu-like symptoms while in the United States.

'What I had was a chronic cough, which I had for the past year. It became worse after the weather in Philadelphia turned very cold and rainy on June 4,' he said. His cough had returned to 'its usual level of mildness' when he left the US and got back to Singapore on June 8.

'I continued to be free of all symptoms apart from my usual cough, which explained why I went about my normal activities. As a point of interest, I did not even cough throughout the duration of the concert which I attended on Saturday,' he added.

He said he also checked his temperature twice a day after returning. 'It was only on Monday afternoon that my temperature was 37.8 deg Celsius. At that point, I called 993,' he said.

A spokesman for A*Star said that after the researcher's diagnosis had been confirmed, it worked with the ministry to trace his contacts and disinfect his laboratory.

French Embassy official Olivier Guyonvarch said his office was informed by the Foreign Affairs Ministry about the case on Tuesday. The embassy sent the health authorities a list of all those who had attended the reception last Thursday. Embassy staff who were at the reception had taken two days off from work. Their children are also staying home from school for two days. French Ambassador Pierre Buhler will stay home until Monday.

Read the full report in Thursday's edition of the Straits Times