Fifteen years ago, when she was just two years into her infectious diseases training at the Communicable Disease Centre (CDC), she fell victim to the Aedes aegypti mosquito.

'It was very, very bad. I had a prolonged fever, extreme discomfort, and my blood platelet count was very low, so I had to be hospitalised. I'm not sure where I caught it, maybe at home.

'At the time, I knew very little about dengue infections,' said Prof Leo, 47, now clinical director of the CDC and in the front line of efforts to deal with the dengue outbreak.

Five years ago, the mother of three found herself battling the disease up close again - when her eldest daughter, now 16, was stricken.

'It wasn't during an outbreak, and it was a reminder that the danger of dengue is always there - every year,' she said.

Her daughter was hit severely, with almost every possible symptom from fever to vomiting to rashes. Prof Leo chose to care for her at home.

'Sometimes, the best care can be outpatient care. She recovered very well at home,' said Prof Leo.

This double brush with dengue could explain why she is now extra careful, combing every spot in her East Coast area home for possible mosquito breeding, especially with the rise in cases in the area.

'We have to be careful because we live in the heart of a region that is traditionally always the epicentre,' she said, adding that it is not just episodic surges one should worry about but the 'long-term battle with the Aedes aegypti'.

She and others had noticed that dengue cases had started climbing in May - earlier than usual.

Her prediction, at the beginning of this month, that Singapore may have an epidemic outbreak on its hands - possibly its worst since the 1960s - proved to be prescient.

Epidemic levels were reached in the week of June 10, with 401 cases. She feels little relief with the slight dip since: Cases were down to 349 last week.

'These are fluctuations...overall, it is up, and we have to anticipate more cases,' she said.

Dengue is perhaps, by itself, not as frightening as other diseases Prof Leo has tackled - she was very much involved when Singapore was in the grip of Severe Acute Respiratory Syndrome, or Sars, in 2003.

But it is a challenge, she said, especially because there seem to be uncontrollable factors at play, including the extremely hot weather, the change in the strain, and the fact that previously successful strategies do not seem to be working as well.

In any case, high numbers are a challenge in any outbreak situation. Above all, no one at high risk must slip through the net.

'Preventing any one death from occurring is our reward,' she said.

Her dengue tip: Know your enemy. The home is the weakest spot. The Aedes aegypti is a 'silent' attacker which tends to leave no marks and causes little pain or itchiness during or after biting.

'The Aedes aegypti has adapted to living with us. When you have your enemy this close, you have to be very careful - all the time.'