INFLUENZA AND VIRUS INFECTIONS OF THE RESPIRATORY TRACT

Although it is impossible to compute their total frequency, virus infections of the respiratory tract are certainly the commonest cause of illness in Britain. The rise in the notifications of pneumonia during winter, the new claims for sickness benefit under health insurance and the deaths in persons over the age of 65 years reflect the frequency of such infections. The appearance of a more virulent virus such as influenza A swell the figures ; but it is certain that in every winter a number of different viruses play a part in the seasonal epidemic.
People in all age-groups are susceptible to infection, but for those at the extremes of life the illness is particularly hazardous. Respiratory virus infection is not only more common in children under the age of five years but, in the first year of life, the illness is more severe. Indeed, simple involvement of the upper respiratory tract without evidence of pneumonia—what would in the adult be merely a " cold "—can produce in the infant a life-threatening illness. Again, in the elderly, degenerative processes, especially of the heart or lungs, make pneumonia a more frequent and serious complication, and the same can be said for patients at all ages suffering from chronic cardiac disease or chronic bronchitis. It is probable that the majority of the common respiratory viruses reach the mucosa directly from the inspired air. This has two consequences. Firstly, since cellular invasion is direct the presence of humoral antibody is relatively unimportant, at least so far as the initiation of infection is concerned. This may in part explain why immunity to these common infections seems so poor and susceptibility to re-infection throughout life so common. Secondly, vims multiplication in mucosal cells deranges their metabolism and may ultimately destroy them. The alteration to cellular physiology, however, is non-specific. The response of the cell is limited and this means that the signs and symptoms and their localization in the respiratory tract can be the same for a number of viruses. In other words the same virus may produce a variety of illnesses and a number of viruses may produce the same type of illness. This makes a very confusing picture for the clinician, especially as the number of viruses known to produce respiratory infection is continually increasing. The following table lists some of the more important of these viruses but it must be appreciated that each family contains a number of different sere-types.
Precise determination of the responsible virus on the strength of clinical signs and symptoms is thus impossible. Detailed virological examination is required and such methods cannot be applied in every case.
Several factors determine the severity of the illness. The importance of certain host factors has already been mentioned. There is no doubt about the severity of influenza virus infections and this is especially apparent when new antigenic variants of the A type arise as they did for example in 1918 and 1957. Apart, however, from any innate virulence it would seem likely that severity is a measure of the rapidity with which virus can infect large numbers of mucosal cells. Pneumonia may thus occur purely as a result of rapid dissemination of virus throughout the respiratory tract. But in the majority of cases, the appear­ance of complications can usually be explained by a superimposed bacterial infection. The pathogens involved are those which are present in the naso-pharynx. The pneumococcus is the organism most commonly isolated, but in
children, H. influenza and in adults Staph. aureus should be thought of for these produce the most severe illnesses.
Antibiotics have no value in the treatment of the uncomplicated virus infections. Unless there is evidence of pneumonia or other indication of bacterial infection they should not be used. The importance of bacteriological examination in such cases is stressed, for the micro-organism may prove to be resistant to the normal antibiotic of first choice, namely, penicillin.
The incubation period of most of these infections is short—one to two days. Influenza is only notifiable when it is complicated by pneumonia.
Prevention and Epidemiological Control.—There is no method whereby the spread of infection can be prevented. Free ventilation and avoidance of crowds are clearly advisable, but since many people suffering from minor degrees of illness continue with their daily work, the prevalent virus is constantly present in crowded trains and buses, so that the avoidance of contact is virtually impossible.
Killed virus vaccines have a limited place in active immunization against influenza. A major difficulty lies in the fact that the various strains of influenza virus behave differently as antigens. Thus vaccines to be effective must be prepared from strains which are producing the current infections. As the Asian strain of 1957 is still the prevalent virus there is some justification for immunizing selected groups in the population if they are at special risk (e.g. doctors, nurses and the staffs of certain public services) or because of their known susceptibility to severe infection (e.g. persons with chronic pulmonary or cardiac disease). For adults a single dose of ro ml. subcutaneously in October or November is recommended since adults may be assumed to have had some past experience of the virus antigens and the injection has thus a " booster " effect. Virus vaccines prepared from adenovirus strains have been used experimen­tally but their use in the general population is not recommended.
Curative Treatment.—General Management.—Ideally any person with a febrile upper respiratory tract infection should be isolated from the community in bed until the temperature has returned to normal. Unfortunately, mankind is not so tractable, and the ability to " carry on " is regarded as a virtue. There is no specific serum or drug treatment of proven value, so that the main­stay is efficient nursing and treatment of symptoms (p. i). The nursing procedures that require emphasis are the hygiene of the mouth, nose, eyes and skin. For the relief of pain, aspirin and Dover's powder will usually suffice ;
when there is complaint of sore throat, the aspirin should be slowly dissolved in the saliva and gradually swallowed, when it often has a local analgesic effect. Troublesome cough is best relieved by the administration of a sedative such as syrup codeine phosphate. Cyanosis is usually a sign of pneumonia and an indication for oxygen (p. 929).
Antibiotics.—The response of post-influenzal pneumonia to chemotherapy is often unsatisfactory. At least part of the explanation for this is that in severe infections there is extensive damage to the mucosa of the upper respiratory tract and bacterial superinfection is correspondingly great. Two pathogens which have already been mentioned—H. infiuenssce and Staph. aureus—are particularly dangerous secondary invaders and their prompt detection warrants bacterio­logical examination of the sputum from patients with pneumonia during influenza virus epidemics. Tetracycline (2-0 g. during the first 12 hours) is advised as the antibiotic of first choice while bacteriological results are awaited. In the fulminating cases two dangers must be emphasized. In some cases the hasmor-rhagic pulmonary secretion is so profuse that the patient cannot rid himself of it quickly enough and is in danger of suffocation. In others the extensive ulceration of trachea and bronchi results in desiccation with extensive crusting. These patients can be successfully managed by tracheostomy, removal of secretions by suction, nursing in a highly humid atmosphere or even by the use of a mechanical respirator.
Other Complications.—Pyogenic complications may arise in the para-nasal sinuses or middle ear. In this event there is less urgency in beginning treatment, and a bacteriological examination which includes sensitivity testing of any pathogens isolated should precede the onset of treatment. The antibiotic to be used may then be chosen with some precision. Toxic myocarditis must always be borne in mind, especially in the older patient.
Convalescence.—The importance of an adequate period of convalescence after influenza must be impressed particularly upon the older patient. Owing to the toxic effect of influenza on the myocardium it is wise even in the mildest case to advise rest in bed for at least three days after the temperature has settled. This applies particularly to those over the age of 35 years. In more severe attacks this period should be extended to one to two weeks. The response of the heart to increased exertion must be carefully watched, and a further rest enforced if this be unsatisfactory. Cough due to tracheitis is sometimes very persistent, but is usually relieved to some extent by the administration of a teaspoonful thrice daily of either elixir of methadone or syrup of codeine phosphate. Infected nasal sinuses may be the exciting factor and should receive' appropriate treatment.