When children die from flu

We know that the burden of mortality of seasonal influenza falls mainly on the older population but also can kill children and infants. In 2004 CDC started the Influenza-Associated Pediatric Mortality Surveillance System, itself part of a larger notifiable disease system. Its aim was to find out more about the pattern of influenza deaths in children. It is now bearing fruit. A recent surprise was the subject of a CDC Health Advisory, its middle level of broadcast health alerts:

From October 1, 2006 through May 7, 2007, 55 deaths from influenza in children have been reported to CDC from 23 state health departments and two city health departments. Data on bacterial co-infections were reported for 51 cases; 20 (39%) had a bacterial co-infection, and 16/20 were infected with Staphylococcus aureus. While the number of pediatric influenza associated deaths is similar to that reported during the two previous years, there has been an increase in the number of deaths in which both influenza and pneumonia or bacteremia due to S. aureus were identified. (CDC Health Advisory)

Influenza co-infection with S. aureus in pediatric deaths was new, happening only once in the 2004-2005 season and three times in 2005-2006. So this is not only a strong association but a dramatic increase. It also wasn't just any S. aureus, but most (or all? the advisory isn't clear) were Methicillin Resistant S. aureus (MRSA), the antibiotic resistant variety. Comparing the 20 S. aureus co-infection deaths with the 31 others, the S. aureus/influenza cases were considerably older (11 years old versus 4 years old, median age). The co-infected death cases were generally children in good health who progressed rapidly to severe illness and death. There didn't seem to be anything different about the influenza strains involved in comparison to those circulating generally in the community and the S. aureus MRSA strains were typical of strains seen in MRSA skin infections.

S. aureus is a common organism found on the skin and in the nose. Some strains can produce a toxin that causes a common form of food poisoning and S. aureus is typically found in abscesses on the skin and elsewhere. S. aureus was exquisitely sensitive to penicillin (the petri dish in which Alexander Fleming first noticed the inhibiting effects of the mold Penicillium notatum contained S. aureus), but it wasn't long before resistance to penicillin developed (well underway by the 1960s). New antibiotics to get around the resistance then became the mainstay of antibiotic treatment of this common pathogen. Methicillin was one of the first, but there are a number of others. In the 1990s methicillin resistant strains (called MRSA strains) also resistant to many of the other penicillin replacements began to appear in hospital settings, where they are now fairly common. Community MRSA is now also seen with increasing frequency. The source of the MRSA organisms in these pediatric co-infections isn't known, or even whether this is a co-infection (more or less simultaneous), pre-infection with MRSA or MRSA superinfection of an influenza infection. Since S. aureus superinfections are not uncommon in serious influenza, it is likely the latter.

This finding of S. aureus co-infection in pediatric deaths from influenza is another reminder (if we needed one) that the clinical consequences of influenza virus infections are not "just about the sequences" but involve a complex triad of the virus, the host and its status and the environment, including other bugs that might be around.

So much to learn. So little time.