Sentinel physicians such as Prystowsky are on the outlook for increasing numbers of patients with symptoms such as sore throat, fever and cough. The doctors file a weekly report with New Jersey's Local Information Network and Communication System and state health officials analyze the data for spikes in the numbers.
If a suspicious illness appears, the sentinel physician may send a sample to the state labs in Trenton to be tested and forwarded to the federal Centers for Disease Control and Prevention, which oversees the sentinel program.
New Jersey's Pandemic Plan is a "generic" defense against any invading microbe, said Dr. Eddy Bresnitz, the state epidemiologist.
[...] New Jersey will also monitor any "influenza-like illness" reported by hospitals, nursing homes and elementary schools, as well as the amount of over-the-counter drugs sold by pharmacies, as possible early indicators of flu.
Addendum: you should also see the link to the European Influenza Surveillance Scheme provided by a reader in the comments section.