Flu - Tests and diagnosis

Flu epidemics tend to be seen from late autumn until early spring in temperate climates (in warmer climates, fluA viral infection affecting the respiratory system. infectionInvasion by organisms that may be harmful, for example bacteria or parasites. is seen all year round). It can be difficult for doctors to distinguish between influenzaA viral infection affecting the respiratory system. and the other virusesMicrobes that are only able to multiply within living cells. and bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell. that can cause similar symptoms.[1]

Fortunately, it is not always necessary to prove the diagnosisThe process of determining which condition a patient may have. through specific testing, and otherwise healthy people who are thought to have fluA viral infection affecting the respiratory system. may simply be advised to stay at home until they feel better, so limiting the spread of infectionInvasion by organisms that may be harmful, for example bacteria or parasites..

During an epidemicA sudden outbreak of infection that affects a large proportion of a population., people may be prescribed antiviralA substance that acts against viruses, for example and antiviral drug. drugs based on their symptoms alone. However it may be more important to establish a precise diagnosisThe process of determining which condition a patient may have. in people at high risk of complications, or those who develop symptoms at a time when a fluA viral infection affecting the respiratory system. outbreak has not been reported.

Making an accurate diagnosisThe process of determining which condition a patient may have. is more important in people who are admitted to hospital, because they often need antiviralA substance that acts against viruses, for example and antiviral drug. treatment and steps have to be taken to limit the spread of fluA viral infection affecting the respiratory system. within the hospital.[2]

The diagnosisThe process of determining which condition a patient may have. of fluA viral infection affecting the respiratory system. is based on a combination of symptoms and signs, the knowledge of local epidemics and, less often, laboratory testing.[3-5]

Symptoms and signs

Features of having fluA viral infection affecting the respiratory system. that might help to distinguish it from other respiratory tractThe parts of the body that are involved in respiration. The respiratory tract includes the nasal passages, throat (pharynx), windpipe (trachea), bronchi and lungs. infections include:[2]

  • The illness coming on abruptly
  • The time of year it happens (if in temperate climates)
  • The way the illness develops.

During fluA viral infection affecting the respiratory system. season, research has shown that diagnosing fluA viral infection affecting the respiratory system. based on clinical signs and symptoms alone can be very accurate - in other words, laboratory testing for the virusA microbe that is only able to multiply within living cells. is not usually necessary. These signs and symptoms include fever, cough, muscleTissue made up of cells that can contract to bring about movement. pain and chills.[3-5]

One study showed that the features that helped to establish a diagnosisThe process of determining which condition a patient may have. of fluA viral infection affecting the respiratory system. were abrupt attacks of shivering and feeling cold (rigorsAbrupt shivering, often with fever and sweating.), sweating, fever, and an abrupt onset of symptoms.[4]

The features that helped to rule out fluA viral infection affecting the respiratory system. included a lack of systemic symptoms (in other words, bodily symptoms such as fever and malaiseGeneral feeling of being unwell. that are not specifically related to the respiratory system), no cough, and the person having the ability to cope with daily activities.[4]

Learn more about the symptoms of flu.

If your doctor suspects you are infected with fluA viral infection affecting the respiratory system., he or she will probably examine you by taking your temperature, having a look at your throat and listening to your chest. This may help to diagnose fluA viral infection affecting the respiratory system. but still does not help to identify the type of virusA microbe that is only able to multiply within living cells. responsible.[6]

Knowledge of local epidemics

Being aware of any outbreaks of fluA viral infection affecting the respiratory system. in the same region can be helpful in making a fluA viral infection affecting the respiratory system. diagnosisThe process of determining which condition a patient may have. more likely.[1]

Laboratory testing

During outbreaks of fluA viral infection affecting the respiratory system., laboratory tests may be available to identify influenzaA viral infection affecting the respiratory system. type A and type B virusesMicrobes that are only able to multiply within living cells.. The different tests vary in terms of their accuracy, how long it takes to get the results, the type of specimen analysed and the cost.[1]

The most accurate test, in both young and older people, is one called reverse transcriptase polymerase chain reaction (PCRPolymerase chain reaction, a technique that involves the isolation and analysis of genetic material or DNA.). This test allows the geneticRelating to the genes, the basic units of genetic material. material (DNAThe building blocks of the genes in almost all living organisms - spelt out in full as deoxyribonucleic acid.) of the virusA microbe that is only able to multiply within living cells. to be identified, and can be done on cells taken from the respiratory secretions. These cells are obtained by gently swabbing the back of the throat (a nasopharyngeal swab), and are sent to the laboratory for further analysis.[2]

Other available tests include taking mucus samples and growing the virusA microbe that is only able to multiply within living cells. in the laboratory (known as viral cultureThe growth within a laboratory of microbes, organisms too small to be seen with the naked eye.), although this takes a little longer and so is not as useful in practice, and bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. tests looking for certain antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy..[2,3]

Despite the availability of these tests, further improvements in the detection of specific strains of fluA viral infection affecting the respiratory system. virusA microbe that is only able to multiply within living cells. are still needed.[2]

References: 
  1. Montalto NJ. An office-based approach to influenzaA viral infection affecting the respiratory system.: clinical diagnosisThe process of determining which condition a patient may have. and laboratory testing. Am Fam Physician. 2003;67:111-8.
  2. Mossad SB. 2008-2009 Influenza update: a better vaccine match. Cleveland Clinic Journal of Medicine. 2008;75:865-70.
  3. Newton DW, Treanor JJ and Menegus MA. Clinical and laboratory diagnosisThe process of determining which condition a patient may have. of influenzaA viral infection affecting the respiratory system. virusA microbe that is only able to multiply within living cells. infections. Am J Managed Care. 2000;6(suppl):S265-75.
  4. Ebell MH, White LL and Casault T. A systematic review of the history and physical examination to diagnose influenzaA viral infection affecting the respiratory system.. J Am Board Fam Pract. 2004;17:1-5.
  5. Zambon MC. Epidemiology and pathogenesis of influenzaA viral infection affecting the respiratory system.. Journal of Antimicrobial Chemotherapy. 1999;44:3-9.
  6. DM Fleming. Influenza diagnosisThe process of determining which condition a patient may have. and treatment: a view from clinical practice. Phil Trans R Soc Lond. 2001;356:1933-43.