A Howard County teenager died of the flu this week, the latest of nine pediatric flu deaths nationally this year, county health officials said yesterday. "This tragic death is highly unusual," the county health officer, Dr. Peter L. Beilenson, said in a news release. Federal patient privacy laws prohibit the county from releasing the victim's identity or any details of the case, Health Department spokeswoman Lisa de Hernandez said. The teenager became ill with "flu symptoms that got progressively worse," she said, and died sometime since Sunday in a hospital that she declined to identify. Officials at Johns Hopkins Children's Center confirmed that Zachary D. Weiland, 15, of Mount Airy died there Sunday, but they would give no further information, including his illness.