14.1 Acute upper respiratory infections
Because of their frequency, upper respiratory tract infections (URTIs) are a major burden for young children and their parents. Although the common cold is the most common ailment in humans, it is particularly frequent in preschool-aged children, who average six to eight episodes per year. The timing and frequency of these infections depends on the level of exposure, occurring earlier and more often in those with older siblings, and those who attend daycare (Fig. 14.1.1). The vast majority of URTIs are viral in origin, mild, and of short duration (5–7 days), and usually described as a ‘common cold’. Numerous different viruses are responsible, and the age of the child and the specific respiratory virus are the major predictors of the symptoms, severity and extent of respiratory tract involvement (Tables 14.1.1, 14.1.2).
Fig. 14.1.1 Number of respiratory tract infections per year in infants and preschoolers (daycare versus homecare).
(From data in Isaacs D, Moxon ER 1996.)
Table 14.1.1 Age of child and type of respiratory tract infection
| Age | Type of infection |
|---|---|
| Newborn | Risk of acute, generalized systemic illness with respiratory syncytial virus (looks ‘septic’) |
| Infant | High risk of lower respiratory tract involvement with respiratory viruses (particularly acute viral bronchiolitis from respiratory syncytial virus) |
| Toddler/preschooler | Very frequent viral respiratory tract infections, mostly confined to upper respiratory tract |
| High risk of viral laryngotracheobronchitis (‘croup’) from parainfluenza viruses | |
| School age (5–15 years) | Lower rates of viral respiratory tract infection |
| Suspect: |
Table 14.1.2 Incubation period of viral respiratory infections
| Virus | Median incubation period (95% confidence interval) |
|---|---|
| Influenza A | 0.6 (0.5 to 0.6) days |
| Rhinovirus | 1.9 (1.4 to 2.4) days |
| Parainfluenza | 2.6 (2.6 to 3.1) days |
| Adenovirus | 3.2 (2.8 to 3.7) days |
| Respiratory syncytial virus | 4.4 (3.9 to 4.9) days |
| Influenza B | 12.5 (11.8 to 13.3) days |
Respiratory complications
The importance of these recurring infections of early childhood should not be underestimated. A significant percentage of children will suffer from local complications of viral URTIs, especially acute otitis media and acute sinusitis (Fig. 14.1.2). Moreover, progression of the infection into the lower respiratory tract is a risk, particularly in the very young. This is especially likely with the more potent respiratory viruses, such as respiratory syncytial virus (RSV – the usual cause of acute viral bronchiolitis), parainfluenza (the usual cause of viral ‘croup’), influenza virus (A and B) and the recently recognized human metapneumovirus (HMP – a close relative of RSV). Some children are particularly vulnerable to these lower respiratory tract complications, suggesting additional important host and environmental factors (Fig. 14.1.3).
Systemic complications
As well as their direct respiratory morbidity, viral URTIs can cause serious indirect or systemic complications. For example, respiratory viruses are by far the most common trigger of severe acute exacerbations of wheeze and asthma in young children, resulting in high rates of attendance at emergency departments and hospitalization. Viral URTIs can also trigger vascular syndromes, such as Henoch–Schönlein purpura. Further, it is difficult clinically to differentiate viral pharyngitis (very common – and relatively harmless) from streptococcal pharyngitis (uncommon – but can result in serious complications such as acute glomerulonephritis or rheumatic fever).
Incubation period of viral respiratory infections
Knowledge of the incubation period of these respiratory viruses is useful when considering the likely timing of infection, the source and quarantine decisions. A systematic review of over 400 publications described the median incubation period (and 95% confidence intervals) for the respiratory viruses of public health importance; these are listed in Table 14.1.2. Most have a short incubation period, with symptoms generally developing within 2–3 days of exposure.
Identifiable URTI syndromes
Arbitrary definitions are used to describe the many ‘URTI syndromes’, such as rhinitis, rhinosinusitis, stomatitis, pharyngitis (tonsillitis) and otitis media. These descriptive terms signify the site of predominant symptoms – nose, sinuses, mouth, throat and ear (earache) respectively. Clearly there is substantial overlap with these syndromes, as viral infections ignore anatomical boundaries. Indeed, as a general rule, viral inflammation of the respiratory tract is usually diffuse rather than focal, whereas bacterial infections of the respiratory tract (such as streptococcal tonsillitis) are often more localized anatomically.
The two most common forms of URTI are the ‘common cold’ (with predominant symptoms being nasal) and pharyngitis (predominant symptom being sore throat), which are discussed in detail below.
Common cold (uncomplicated viral URTI or ‘head cold’)
This is defined as an acute illness where the major symptoms are:
The symptoms are mild, fever is often minimal or absent, and all symptoms resolve between 5 and 7 days. The usual pathogen responsible for an uncomplicated viral URTI is rhinovirus, which has over 100 types. However, there are many other respiratory viruses that can produce this syndrome (see Table 14.1.2). These viruses are highly infectious and spread via both droplets (particularly by sneezing) and nasal secretions on hands and fomites (clothing, handkerchiefs, toys, cot sides). Viral shedding is maximal in the 7 days after inoculation and most have a short incubation period (2–3 days). Therefore, close proximity such as household contacts with older school-aged siblings, daycare attendance, overcrowding, lower socioeconomic status and poor personal hygiene are all associated with higher rates of URTI (see Fig. 14.1.3).
Local ENT complications of the common cold include otitis media and acute rhinosinusitis (see Fig. 14.1.2), and a small proportion progress to involve the lower respiratory tract.
Pharyngitis (oropharyngitis/tonsillitis)
Pharyngitis is a clinical syndrome in which the major complaint is acute sore throat and/or discomfort on swallowing (dysphagia). The illness is common, generally mild and self-limiting, with three-quarters of patients free of pain within 2–3 days of onset, whether due to a respiratory virus or to β-haemolytic streptococcus. Many respiratory viral infections begin with a sore throat, before the development of the more obvious symptoms and signs such as rhinorrhoea/sneezing. However, there are a number of specific, recognizable syndromes of oropharyngitis/tonsillitis, which are described briefly below.
Ulcerative pharyngotonsillitis
This is usually due to an adenovirus infection and typically occurs in infants and toddlers. It produces an isolated exudative tonsillitis resembling streptococcal tonsillitis or Epstein–Barr virus pharyngitis. Adenoviruses (types 3, 4, 7, 14 and 21) also produce the very specific ‘pharyngoconjunctival fever’. The enteroviruses (Coxsackie virus and echovirus) and herpes simplex virus can also produce ulcerative pharyngotonsillitis. Other respiratory viruses (including RSV and parainfluenza) usually cause a more diffuse nasopharyngitis rather than this focal tonsillar inflammation.
Epstein–Barr virus pharyngitis/tonsillitis
Although this typically occurs in older, school-aged children, it can also cause an exudative tonsillitis in the very young. The tonsillitis is associated with a membrane and marked cervical lymphadenopathy. Generalized symptoms, including fever, lethargy, anorexia and headache, can also occur, especially in older children and adolescents, and the condition is usually referred to as infectious mononucleosis, or ‘glandular fever’.
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