Respiratory Syncytial Virus in children. 93/3

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Respiratory Syncytial Virus (RSV) is ubiquitous and almost all children have been infected at least once by the age of five years. It is a major cause of respiratory illness in children and may cause bronchiolitis, pneumonia, croup, tracheobronchitis and upper respiratory tract illness, sometimes accompanied by otitis media. Infection may be life-threatening in young infants, particularly those with underlying disease such as cardiopulmonary or congenital disorders.

Naturally acquired immunity to RSV is incomplete and reinfections with RSV may occur throughout life, although subsequent infections may cause less severe illness.

Although no comprehensive information is available on the occurrence of RSV infection in the population, laboratory reports sent to the Public Health Laboratory Service (PHLS <sources.htm#other>) Communicable Disease Surveillance Centre (CDSC) by Public Health and other hospital laboratories throughout England and Wales provide some indication of trends and the distribution of RSV infection. Further information on outbreaks is provided by hospital admission data for clinical syndromes associated with RSV.

Age and sex distribution

The vast majority (88%) of laboratory reports of RSV infection relate to illness in children under one year or age (figure 1). In this age group, infection is more commonly reported in boys than girls although the excess may reflect sex differences in the severity of symptoms rather than sex differences in infection rates.

Figure 1: Age and sex distribution of laboratory reports of RSV

Reported RSV infections peak in infants aged one month and decline steadily thereafter (figure 2). Again this may reflect disease severity rather than the pattern of infection.

Figure 2: RSV laboratory reports by age

Older children and adults may also be infected more frequently than laboratory reports suggest, but symptoms tend to be less severe in these age groups and consequently such patients are examined and treated less frequently.

Clinical manifestations

Bronchiolitis and pneumonia are the most commonly reported conditions associated with RSV infection in pre-school children.

Figure 3: Reported clinical features associated with RSV infection in children

Seasonal patterns

Annual outbreaks of RSV occur each winter and are reported from all areas of the country each year. Laboratory reports of RSV in England and Wales as a whole typically peak in December or January, but the timing of the onset of the outbreak may vary from region to region.

Figure 4: Reports of infections due to RSV in children under 5

These outbreaks of RSV cause annual epidemics of bronchiolitis and pneumonia in young children and paediatric hospital admissions for these conditions show marked winter peaks (note that the apparent upward trend in hospital admissions may be wholly or partly attributable to improvements in the completeness of hospital admission data over the period shown).

Figure 5: Paediatric admissions for bronchiolitis and pneumonia, children

The increase in hospital admissions for RSV related conditions appears to precede the increase in laboratory diagnosis and reporting.

Summary

• Outbreaks of RSV occur each winter and affect all areas of the country.

• Almost all children have been infected at least once by the age of five years.

• Young infants tend to be the most severely infected; the vast majority of RSV infections reported by the public health and hospital laboratories relate to infections in children aged less than one year.

• Infection and reinfections are also common in older children and adults but symptoms tend to be less severe at older ages, except in the elderly and those with other underlying disease.

• Bronchiolitis and pneumonia are the most commonly reported conditions caused by RSV infection in children.

• Paediatric hospital admissions for RSV related conditions increase markedly during outbreaks of RSV.