I had swine flu. It is almost a badge of honor, suggesting that the speaker survived the first pandemic of the 21st century and is immune to the next wave.

It also may be wrong.

Tests at Children's Hospital of Philadelphia suggest that large numbers of people who got sick this fall actually fell victim to a sudden, unusually severe - and continuing - outbreak of rhinovirus, better known as a key cause of the common cold.

Experts say it is logistically and financially impossible to test everyone with flulike symptoms. And signs, treatment, and prognoses for a bad cold and a mild flu are virtually identical, so the response hardly differs.

But the finding may send an important message to parents who (despite doctors' recommendations) are questioning the need to immunize their children against swine flu because they seemed to have already had the disease, said Susan Coffin, director of infection prevention and control at Children's Hospital.

"Maybe their child is still susceptible to H1N1 and should still get the vaccine," Coffin said.

For years, rhinoviruses have been the Rodney Dangerfields of microbes. Even major institutions have found plenty of reasons not to pay them much mind. They are exceedingly common, they cause mere colds, they come in hundreds of hard-to-identify strains that make testing a challenge, and there is no effective treatment anyway.

Neither the federal government nor the states track rhinoviruses in the way they do "surveillance" for influenza, based on samplings of doctor diagnoses, emergency-room visits, and lab reports. Children's Hospital of Philadelphia is one of the few institutions that routinely checks for them whenever it tests for influenza and other viruses.

Rhinovirus - named after the Greek word for nose - is known to circulate year-round, and typically to peak shortly before and after flu season. Children's recorded rising numbers in September, right on schedule. Then they kept rising.

"The rate of activity was unbelievably high," Richard L. Hodinka, director of the clinical virology laboratory, said yesterday. "What got my attention was not only the numbers we were seeing in the laboratory, but physicians saying there was severe disease."

'Looking back ...'

The hospital alerted the Philadelphia Department of Public Health. The city, citing reports from several labs, issued an advisory for the public-health community Oct. 9. They also asked the U.S. Centers for Disease Control and Prevention to investigate the outbreak; a CDC team returned to Atlanta last Wednesday after two weeks here but has not finished its analysis.

Meanwhile, people around the region were coming down with flulike illnesses. Two Catholic high schools, Archbishop John Carroll in Radnor and Bishop Shanahan in Downingtown, briefly closed after a third of the students were absent.

Doctors and hospitals had been expecting and preparing for swine flu. Yet laboratory data indicate that, while swine flu was present in the region as early as mid-September, it did not start to rise sharply until the third week of October.

"When this began happening, we all believed what we were seeing was influenza," said Coffin, speaking both as a physician and as the mother of a 16-year-old Lower Merion student who got sick in the middle of September.

"I went around telling my friends, 'I'm positive she had flu.' And now, looking back, I think she probably had rhinovirus."

Lab positives for rhinovirus at Children's continued at very high levels through October as swine flu also spiked. Emergency-room visits for flulike illness spiraled upward.

The ER was forced to convert part of the hospital's atrium lobby into a waiting area, and visits reached a record Oct. 26. (They have been gradually declining since then, and now are about 20 percent more than normal for this time of year.)

Although most ER patients were not tested, late October coincided with the laboratory's highest numbers for both swine flu and rhinovirus. More than 40 percent of them were the latter.

Besides the sheer numbers of rhinovirus, Coffin was surprised that it was causing more problems - wheezing, pneumonia, fever, and lower-respiratory-tract infections - than are normally associated with the common cold, which typically infects the upper respiratory tract. That has led her to suspect that a strain not seen here before may be responsible. The CDC's lab will attempt to identify the strain.