Bug war

MRC scientists have recently discovered that a significant proportion of pneumonia in children is not caused by a virus, but by a bacterium - the pneumococcus. This has important implications for the treatment of children.

World Health Organisation statistics state pneumonia as the leading cause of death in children worldwide. Almost four million children die of the disease each year - most of them in developing countries.

Almost a year ago, scientists from the MRC's Respiratory and Meningeal Pathogens Research Unit proved that a 9-valent pneumococcal vaccine significantly reduced pneumonia, pneumococcal disease and antibiotic-resistant pneumococcal disease among forty thousand infant trial participants in Soweto. An added bonus was that the vaccine also showed promise in the treatment of HIV-positive infants.

Now further analysis of trial results has shown that 31% of children's pneumonias, previously thought to be caused only by viruses, are in fact caused by a bacterium. This was proved by the fact that the pneumococcal vaccine prevented viral-associated pneumonia in the children.

According to Prof Keith Klugman, the director of the unit, the findings are important for a number of reasons. "They show that children in hospital with severe pneumonia need antibiotics."

A viral illness (such as a cold or flu) is not treated with antibiotics; this medication is only effective for a bacterial infection. The reason is that antibiotics target the cell wall and metabolism of bacteria, and a virus does not have a cell wall. Since viruses also have different metabolic pathways to bacteria, antibiotics are completely ineffective.

"Up until now, the emphasis has been to try and find out whether the infection was caused by a virus or a bacterium before starting treatment. But this shows that by the time a child reaches hospital, the virus and the bacterium are working together, so treatment with an antibiotic will be effective."

The results have been very encouraging: Prof Klugman says the vaccine is better at preventing pneumonia than was previously thought.

The results also show the extent of the collaboration between viruses and bacteria in causing human illness. "Our evidence shows that what starts out as a viral infection often ends in a bacterial infection. We think that between one third and one half of all viral pneumonia infections are actually caused by the pneumococcus bacterium. The results show that the vaccine reduces pneumonia associated with respiratory viral infections, because it prevents the bacterium from infecting a child who might already be struggling with a viral infection."