Routine tests for human influenza A will be positive in patients with bird flu but are not specific for the avian virus. To make a specific diagnosis of bird flu, specialized tests are needed. In the United States, local health departments and the Centers for Disease Control and Prevention (CDC) can provide access to the specialized testing. The virus can be detected in sputum by several methods, including culture or polymerase chain reaction (PCR). Cultures should be done in laboratories that have an appropriate biosafety certification. PCR detects nucleic acid from the influenza A virus. Specialized PCR testing is available in reference laboratories to identify avian strains; the CDC is a primary source for available tests for the newest strains of bird flu and can identify the specific type of virus (for example, H5N1 or H7N9). During and after infection with bird flu, the body makes antibodies against the virus. Blood tests can detect these antibodies, but this requires one sample at the onset of disease and another sample several weeks later. Thus, results are usually not available until the patient has recovered or died.