Viral infections are much more common than bacterial ones in children diagnosed with pneumonia, and respiratory syncytial virus is the most common cause, suggests a study of patients across Utah and Tennessee.

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Vaccination has brought down the rate of childhood pneumonia caused by bacteria, but other causes need to be better understood and continue to result in hospitalizations.

The Etiology of Pneumonia in the Community (EPIC) study was led by the US Centers for Disease Control and Prevention (CDC) in collaboration with University of Utah Health Sciences, with results published in the The New England Journal of Medicine.

A total of 2,638 children with symptoms of pneumonia were enrolled in the study between July 2010 and June 2012, at Primary Children’s Hospital in Salt Lake City, UT, and in TN, Le Bonheur Children’s Hospital in Memphis, and Monroe Carell Jr. Children’s Hospital in Nashville.

Pneumonia was confirmed by X-ray in 2,222 children and their body fluid samples were tested for bacterial and viral pathogens. Children with recent hospitalization or severe immunosuppression were excluded from the analysis.

Viral infections were much more common than bacterial infections in the children in the study that had been diagnosed with pneumonia – 73% compared with 15%.

Co-investigator Dr. Andrew Pavia, chief of the division of pediatric infectious diseases at University of Utah School of Medicine, says vaccines have lowered the rate of bacterial infections, adding that it is important to understand the causes and etiology behind the hospitalizations that continue to result from childhood pneumonia.

“Over the last 3 decades, introduction of Haemophilus influenzae type b and pneumococcal conjugate vaccines has significantly lowered the incidence of bacterial pneumonia in children,” Dr. Pavia says.

“Our results are consistent with previous findings, and support continuing immunization efforts to maintain the reduction in bacterial pneumonia.

“It’s also important to understand how causes of pneumonia have changed so we can better approach the illness, which still leads to high rates of hospitalization among children.”

The researchers remind us there is a spike in community-acquired pneumonia during winter, because its spread is facilitated by people being in closer contact as they retreat indoors. The lung infection triggers:

  • Persistent coughing
  • Chest pain
  • Fever
  • Difficulty breathing.

Community-acquired pneumonia is “particularly hard on the very young and the very old,” the authors say – “in fact, pneumonia is the leading cause of hospitalization among US children, with estimated medical costs of $1 billion annually.”

“Despite this large burden of disease, critical gaps remain in our knowledge about pneumonia in children,” reads the study introduction.

Chris Stockmann, co-investigator and senior research analyst at the University of Utah, says of the study:

“The results help define the role of viruses as major players in pediatric pneumonia and shows a need for new therapies that can reduce the severity of viral pneumonia.”

More than a dozen bacterial and viral pathogens were found in the children in the study, causing a fifth, 21%, to need treatment in intensive care.

Respiratory syncytial virus (RSV) was the most commonly detected pathogen, and affected the under-5s more than older children (37% versus 8%).

Children under the age of 5 years were also more vulnerable to:

  • Adenovirus (15% versus 3% in older children)
  • Human metapneumovirus (15% versus 8%).

The authors conclude:

Effective antiviral vaccines or treatments, particularly for RSV infection, could have a mitigating effect on pneumonia in children.”

The very youngest children were more likely to need hospital – half of all the children hospitalized with pneumonia in the study were aged 2 years or younger.

In children between 5 and 18 years of age, the most common pathogen was a bacterium, Mycoplasma pneumonia – 19% in the over-5s versus 3% in the under-5s.

Rhinovirus – the predominant cause of the common cold – was the second most commonly detected pathogen among children with pneumonia.

“Interestingly,” the researchers say, rhinovirus was also found in a large proportion of the children who had no symptoms, who were acting as controls in the study.

Rhinovirus was found in 22% with pneumonia, compared with 17% without, and “one interpretation is that rhinovirus infections do not commonly lead to pneumonia. Another is that some types of rhinoviruses cause a runny nose, while others cause severe pneumonia that leads to hospitalization.”

The study authors give an estimate of the total annual incidence of hospitalization for community-acquired pneumonia.

By combining their data from the three study hospitals, they estimate a rate in children under 18 years of age of just under 16 cases for every 10,000 children in the population.