The clinical symptoms of influenza are fairly characteristic, and during periods of epidemics enable a sufficiently reliable diagnosis to be made. For general practitioners, they form the basis for diagnosing influenza. During differential diagnosis, account must be taken of conditions such as: the common cold, infections caused by other types of viruses and bacterial infections. The following information sources help when making a clinical diagnosis:
- epidemiological bulletins informing about an increased incidence of influenza cases,
- results of epidemiological observations made by the doctor (increased visits by patients with clearly defined clinical symptoms),
- data from the case history confirming contact between the patient and a person suffering from influenza.
Virological and serological diagnosis
In non-epidemic periods and in clinically doubtful cases during epidemics, there is the possibility of using laboratory diagnostic methods. Rapid “bedside” diagnosis tests give confirmation of the presence of influenza virus within 15-30 minutes. The usefulness of the tests is limited due to their moderate level of sensitivity and specificity. Virological diagnosis confirms the presence of the virus in material collected from the patient. The following tests are conducted: 1.immunofluorescent (IF) and immunoenzymatic (ELISA) tests – time required for result: 1 day. 2.RT-PCR tests or in situ hybridization – detection of viral RNA. Time required for result: up to several days. This method is sensitive and specific, but expensive. It is the reference method in difficult cases. 3.cultivation of the virus in chicken embryos or tissue cultures – time required for result: ten days or more. This method is used mainly during inpatient treatment and for the purposes of epidemiological monitoring (sentinel programme). Serological diagnosis confirms infection with influenza virus post factum based on identification of an increase in antibody titres in the patient’s serum – haemagglutination inhibition test and immunoenzymatic test (ELISA). These are used mainly in retrospective analysis.