Diagnosis of Swine Flu

Swine flu, caused by the influenza virus H1N1 2009 strain, is usually a mild illness. Diagnosis may be made based on the signs and symptoms of the disease. Swine flu manifests in most people as a usual flu infection with similar symptoms and thus may be confused with other viral illnesses.

H1N1Image Credit: Tashatuvango / Shutterstock.com

Features of swine flu

According to the Centers for Disease Prevention and Control (CDC) guidelines, swine flu is diagnosed in presence of the following features:

  • Acute fever and airways infection within 7 days of close contact with a person who has been confirmed to be a case of H1N1 influenza A infection
  • Acute fever and airways infection within 7 days of travel to a community (within or outside the country) where there have been one or more confirmed cases of H1N1 influenza A infection
  • Acute fever and airways infection seen in a person living in a community where there is at least one confirmed case of H1N1 influenza A infection

Confirmation of the diagnosis

To confirm the diagnosis, specific laboratory tests are needed that can also detect the strain causing the condition.

Laboratory tests include blood tests, chest X-rays and so forth.

Routine blood tests

Viral infections usually do not cause many changes in the routine blood picture.

A bacterial infection leading to flu-like features may be ruled out using a routine blood test with hemoglobin, complete blood counts including white blood cells, red blood cells and platelet counts.

Chest X-ray

Chest X-rays and other imaging tests are suggested in individuals at risk of complications like pneumonia.

Nose or throat swab

To test for swine flu a nose or throat swab is taken. Within 15 minutes, the laboratory may tell if influenza type A or B is present.

The specimen of the infected material from the patient’s throat or nose is collected within the first 4 to 5 days of illness. This is the most infectious period of the disease and the infected person is most likely to be shedding the virus. Children, however, may shed the virus for 10 days or longer. Further details of the exact strain may take a few days to detect and report.

If there is a wide-spread infection, there may be no need for testing. Treatment is based on the symptoms alone.

Most state health departments, after the pandemic, are now equipped with tests for non-human influenza virus strains. However, if a variant influenza virus is suspected, it is sent to CDC for further testing.

Kit to diagnose influenza

The CDC developed a new kit to diagnose seasonal flu as well as the flu viruses that could become pandemic. This was approved by the FDA (Food and Drugs Administration, USA) in September 2011.

It is called the Human Influenza Virus Real-Time RT-PCR Detection and Characterization Panel (rRT-PCR Flu Panel) and gives results in 4 hours.

The kit can identify and differentiate between influenza A and B viruses, further classify influenza A viruses by subtype, and also detect highly infectious avian or bird influenza A (H5N1) virus infection in human samples.


Further Reading

Last Updated: Nov 4, 2022

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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