Laboratory diagnosis of swine flu: a review

Figures & data

Figure 1. Diagrammatic representation of symptoms of swine flu (H1N1).

Figure 2 A. Worldwide status of swine flu outbreaks. B. Percent occurrence of swine flu in population of various countries.

Figure 3. Antigenic drift of influenza A virus analyzed using monoclonal antibodies.

Table I. Summary of the different methods for detection of Influenza A (H1N1).

Method of testing	Samples	Procedure	Drawbacks
Viral culture	Viral throat or nasal swab	A viral culture is a laboratory test in which samples are placed with a cell medium that the virus being tested for is able to infect. If the cell medium shows changes, then a culture is positive.	Virus isolation is a sensitive technique, but typically requires 5–7 days for testing.
Rapid antigen	Endotracheal aspirate and Bronchoalveolar lavage (BAL) fluid	Rapid antigen tests are best used within the first 48 hours of symptoms to help diagnose influenza and determine whether or not anti-viral medications should be used, or they are ordered within the first week to help identify outbreaks. Viral cultures are usually used to track flu outbreaks and to identify the particular strain that is causing them.	Antigen capture immunoassays, such as the commercially available Directigen tests, can provide rapid test results, but suffer from low sensitivity and high cost.
Direct immune fluorescence (DFA)	Nasal or nasopharyngeal specimens	Direct fluorescent antibody (DFA or dFA) also known as “Direct immunofluorescence” is a laboratory test that uses antibodies tagged with fluorescent dye to detect the presence of microorganisms. This method offers straight-forward detection of antigens using fluorescently labeled antigen-specific antibodies.	DFA lacks sensitivity and specificity. DFA is generally not accepted as a proof of infection in notifying countries (Whiley et al. 2009). The performance of immunofluorescence assays requires laboratory expertise in the methodology and experienced technicians trained in immunofluorescence microscopy.
RT-PCR	Nasopharyngeal aspirate	In testing laboratories, the viral sample is cultured and set up for PCR testing. Using techniques which amplify and simultaneously detect specific nucleic acid sequences, rapid detection of viral nucleic acid sequences is achieved. The reliable technique is called real time polymerase chain reaction [RT-PCR] and the result is available within 24 hours (Carr et al. 2009).	RT-PCR is becoming more commonly available in veterinary diagnostic laboratories, but requires expensive equipment and appropriate laboratory facilities. While the time to get test results can be in as little as 3 hours, routine surveillance samples are more often processed in 24 hours.

Figure 4. Diagrammatic illustration of immunofluorescent antibody testing.

Whiley DM, Bialasiewicz S, Bletchly C, Faux CE, Harrower B, Gould AR, Lambert SB, Nimmo GR, Nissen MD, Sloots TP. 2009. Detection of novel influenza A(H1N1) virus by real-time RT-PCR. J Clin Virol. 45:203–204.

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Carr MJ, Gunson R, Maclean A, Coughlan S, Fitzgerald M, Scully M, et al. 2009.Development of a real-time RT-PCR for the detection of swine-lineage influenza A (H1N1) virus infections. J Clin Virol. 45:196–199.

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