The upper respiratory tract is the initial site of infection or a site of colonisation for most infections of the respiratory tract. It is also the site for a number of resident organisms, the prevalence of which will vary in individuals. Some of these resident flora have the propensity to be pathogenic. Infections of the upper respiratory tract (URTIs) are the commonest acute illness.
Common colds / rhinitis Children suffer 2-6 colds per year in industrialised countries, with this frequency halving in adulthood. This high incidence of colds is attributable to the high number of viruses and serotypes involved. Both aerosol and fomite transmission contribute to spread of infection.
The principal findings of rhinorrhoea and sneezing are found in almost all cases. In addition there may be sore throat, headaches and constitutional upset with fever. Earache is
frequent in childhood. The diagnosis of the syndrome is clinical; laboratory identification is
not required because of the current absence of appropriate antiviral therapy. Anti-rhinoviral therapy is, however, a possibility as drugs are developed that block the interaction between the major host cell receptor (ICAM-1) and the virus anti-receptor in a canyon that occurs on the surface of the viral capsid. Symptomatic therapy with analgesics and decongestants is commonly employed. Vaccine development is hindered by
the diverse aetiology.
Influenza Unlike common colds, which are non-life-threatening illnesses, much mortality
is attributable to influenza, particularly in the elderly and those with underlying cardiopulmonary disease. Clinically, there are three features that distinguish influenza infection from common colds: an acute onset, presence of a fever in almost all cases (occurs in the minority of common colds) and more marked constitutional upset with myalgia. Amantadine and rimantadine are used in the treatment and prophylaxis of influenza A infections. A vaccine is recommended for patients with underlying chronic cardiopulmonary disease, chronic renal failure, or diabetes mellitus, and in the
immunosuppressed. This vaccine is changed annually because the virus undergoes genetic
change either through minor sequence changes (resulting in ‘antigenic drift’) or through
recombination (resulting in ‘antigenic shift’) which produce changes in one or both surface
proteins, the haemagglutin (H) or neuraminidase(N). Antigenic shift increases the likelihood of a widespread pandemic, as even partial prior immunity to a completely new strain is absent.
Sore throat / pharyngitis and tonsillitis Over two-thirds of sore throats are viral in aetiology and may be a continuum of infection of the nasal mucosa (common cold). Streptococcus pyogenes is the commonest bacterial cause and can be associated with severe complications.
Diphtheria is caused by Corynebacterium diphtheriae. There is much local inflammation of the nasopharynx, with a characteristic ‘bull neck’ appearance from enlarged lymph nodes. Toxigenic strains of C. diphtheriae produce a polypeptide that causes local destruction of epithelial cells and spreads systemically to cause myocarditis and polyneuritis.
The aetiological diagnosis is made by culture of a throat swab or by serological assays. With
diphtheria, toxin production should also be sought. Most viral sore throats are self-limiting
and are managed symptomatically. S. pyogenes infections should be treated (most frequently with a penicillin) to prevent complications. Diphtheria toxin can be neutralised with antitoxin. Contacts of diphtheria should be screened and given booster vaccination and/or chemoprophylaxis as appropriate.
Sinusitis / acute otitis media These conditions are most frequently a complication of common colds but may also be due to secondary bacterial invaders. Localised pain is the most frequent symptom, but children with otitis media may present with unexplained fever or vomiting. If chronic infection results, surgery may be necessary in addition to antibiotics.
Epiglottitis This is most commonly a disease of young children as a result of spread of bacteria from the nasopharynx. Haemophilus influenzae type b is the classic cause, but other bacteria may now be more frequent. Bacteraemia is frequent, and epiglottitis may present as an acute medical emergency with respiratory obstruction. Antibiotics may need to be given intravenously.
Tracheitis / laryngotracheitis This causes hoarseness and retrosternal discomfort on both inspiration and expiration. Parainfluenza (and other) viruses cause swelling of the mucous membrane that results in inspiratory stridor, termed ‘croup’. Diagnosis of the specific aetiology is made by identification from a throat swab or serologically.