The first convincing record of a pandemic of influenza was an outbreak in 1580, which actually started in Russia and spread through Africa to Europe. More than 8,000 people were killed in Rome, and several Spanish towns were almost destroyed. The most lethal outbreak was the flu pandemic (H1N1 subtype) of 1918 (Spanish flu pandemic) that spanned from 1918 to 1919. The number of deaths was not precisely known but was estimated to range from 50 million to 100 million.
Influenza virus tests are recommended for all suspected influenza patients who are admitted to the hospital. Clinicians should most relevantly know the limitations of influenza virus tests and how to interpret data correctly, especially the negative results. Rapid molecular testing is a type of molecular influenza diagnostic test to detect nucleic influenza virus acids in highly sensitive and specific specimens of the upper respiratory tract. Quick molecular tests with FDA cleared are available which produce results in about 15- 30 minutes. Some of these speedy molecular tests are for point-of-care use with CLIA. Rapid influenza diagnostic tests (RIDTs) detect viral antigens with 50-70 percent accuracy and high specificity in 10- 15 minutes. Some RIDTs use a reader-analyzer to optimize results to increase sensitivity. Influenza virus antigen detection does not necessarily imply the detection of viable infectious virus or the ongoing replication of influenza virus. Immunofluorescence tests are antigen detection tests that usually require the use of a fluorescent microscope to deliver results with moderate sensitivity and high specificity within 2-4 hours. For the detection of viral antigens of influenza A and B in respiratory tract specimens, both direct (DFA) and indirect fluorescent antibodies (IFA) are available. Subtyping of influenza A viruses by immunofluorescence tests is not possible. A quick immunofluorescence test is an RIDT and uses an analyzer to deliver results in about 15 minutes.
When human influenza A virus (avian influenza A or swine A virus) is suspected of having a virus of animal origin, RT-PCR for seasonal influenza viruses and novel influenza A viruses should be contacted by the local and state health department. Commercially available diagnostic tests for influenza A do not explicitly detect novel influenza A viruses and a positive influenza A virus does not differentiate seasonal influenza A from avian or swine influenza A infections. The results should be assessed in the context of other epidemiological and clinical data available to healthcare providers, just like any other diagnostic test.