MANILA, Philippines?Health Secretary Francisco Duque III declared on Tuesday a ?low-level? community outbreak of the Influenza A(H1N1) virus in certain parts of Metro Manila, as the number of confirmed cases neared the 500 mark. Hundreds more suspected cases are waiting to be officially tested.

Duque said the virus transmission had apparently gone beyond ?third generation? in the communities where affected schools were located.

He mentioned Quezon City, Parañaque and Manila as sites of low-level community outbreak. These, along with Makati, have the highest number of swine flu cases based on the place of residence.

?We?re there but it?s low-level,? Duque said at a news briefing when asked if a community-level transmission already existed after the Department of Health (DOH) confirmed 28 new cases that brought the total to 473.

A community-level outbreak is the fourth and highest level of transmission.

It is no longer possible to trace where the transmission started (called the index case) since the virus has spread beyond the close contacts (called the second transmission cases) and then to more contacts (called the third generation transmission cases).

Duque said the DOH had not observed a ?sustained? community outbreak in Metro Manila.

7-month-old baby

Among the 28 new confirmed cases yesterday was a 7-month-old Filipino infant who became the youngest infected person to date since the first case was detected on May 21.

Like the infant, all the rest of the new patients have not been abroad.

Duque said all the new cases were ?mild? and were receiving treatment.

Health Undersecretary Mario Villaverde said the DOH could no longer distinguish if the new cases were second-generation or third-generation.

Since the very young and the elderly are among the high-risk groups, the DOH is giving special attention to the infant to ensure there will be no complications, according to Duque.

The country had its swine flu-related death in a 49-year-old mother with a preexisting chronic heart disease and various ailments. She died on June 19 just two days after the onset of flu symptoms.

In declaring a ?low-level? community transmission in parts of Metro Manila, Duque said there was no clustering of cases.

?You can put it this way: where the schools are, you already have school-community transmission but still very limited in number,? he said.

Duque said that ?numbers-wise and percentage-wise? the situation was not alarming.

?When you?re given 22 schools that are affected but we have schools between 40,000 and 60,000, that only represents a miniscule number of schools. And consider the total number of persons affected compared to the total population,? he said.

Villaverde said the best thing to do when some of the cases were already third generation was ?to shift to mitigation and to just look for those who are ill and treat them.?

However, in areas where there are no or few confirmed cases so far, DOH field personnel will still do contact tracing to contain the further spread of the virus by advising household members to go into self quarantine.

Much higher

Health authorities have conceded that the total cases in the country is much higher than those they have already confirmed, since the virus spreads much faster than authorities can perform the tests.

All specimens must go through the Research Institute for Tropical Medicine (RITM) in Muntinlupa for confirmatory testing.

Because the number of people asking to be tested is increasing, the DOH is preparing San Lazaro Hospital in Manila and Vicente Sotto Memorial Medical Center in Cebu to take some of the load off the RITM.

The DOH estimated that the spread of the swine flu virus could be likened to the seasonal flu virus which infects about one out of five members in a household and seven to 10 persons in a medium-size community with a population of 1,000.