Bacterial coinfections boosting child flu deaths

Oct 7, 2008 (CIDRAP News) – The number of children who have died from a combination of influenza infection and bacterial pneumonia—in many cases due to the superbug methicillin-resistant Staphylococcus aureus (MRSA)—has risen sharply over the past few years, federal epidemiologists say in a new report that urges flu shots as a preventative.

Overall, the researchers say, child deaths from influenza are relatively uncommon. There were 166 between autumn 2004 and spring 2007, according to a new national reporting system, only a few more than the 153 that occurred in the harsh 2003-04 flu season and prompted the reporting system's founding. But child deaths from flu are rising, and serious complications from bacterial infections such as MRSA are playing a much larger role.

Staph infection is difficult to prevent: The bacterium lives on the skin and in the nostrils and causes disease unpredictably. But "you can't have this overwhelming catastrophic complication without also having the flu, so if you can prevent the flu, you can prevent the coinfection," Lyn Finelli, DrPH, chief of influenza surveillance at the Centers for Disease Control and Prevention (CDC), said in an interview.

Finelli is lead author of the report in the October issue of Pediatrics, which is co-authored by flu and MRSA researchers from two CDC divisions. The article analyzes reports of child deaths from flu filed by 39 states and two local health departments since the CDC made child death from flu a nationally reportable illness in 2004.

Issue emerged 4 years ago
The rate at which children die because of flu is thinly researched; it emerged as an important health issue only after the 153 deaths in the 2003-04 season were tallied. Up to that point, modeling based on flu surveillance reports and death-certificate data had estimated that 28 to 92 children younger than 5 died of flu each year in the United States.

The new surveillance system, which the authors acknowledge does not yet report all deaths, found 47 child deaths from flu in the 2004-05 season, 46 in 2005-06, and 73 in 2006-07, all relatively mild flu seasons. (Preliminary reports from 2007-08, not included in the paper, have identified 86 deaths.) The deaths were very rapid: 45% of the children died within 72 hours of their first symptoms and 75% died within a week, while 43% died either at home or in an emergency room.

Bacterial infection superimposed on flu was not the only cause of death; children also died from seizures, encephalitis, and shock. But it played an important role: Coinfections were involved in 6%, 15%, and 34% in the three successive seasons, a fivefold increase. Almost all of that increase was due to S aureus: There were one staph infection in 2004-05, 3 in 2005-06, and 22 in 2006-07, and 64% of the staph infections were drug-resistant.

(Oddly, very little illness was attributed to Streptococcus pneumoniae [pneumococcus] historically the No. 1 cause of pneumonia in children—a finding that may reflect the influence of new pneumococcal vaccines.)

Staph pneumonia is not a new phenomenon; from 3% to 10% of pneumonias that begin outside hospitals have been attributed to staph, but those pneumonias tend to occur in the elderly and immune-impaired. And the severity of simultaneous staph and flu infections has been documented after each influenza pandemic, in which large numbers of deaths were attributed to bacterial pneumonia.

But the staph pneumonias recorded by the new reporting system represent an apparently new development, because they occurred in previously healthy children infected with a seasonal flu virus that presumably does less damage to the lungs and immune response than a novel pandemic one. And they appear to be occurring at the same time as a rapid rise in MRSA colonization in the United States, which doubled between 2001 and 2004.

Most victims weren't vaccinated
A troubling aspect of the report is that most of the children who died had not been vaccinated against flu, which would have protected them from primary viral onslaughts such as encephalopathy, as well as from the lethal synergy of flu and bacterial infection. Ninety of the 166 had an underlying condition such as asthma or a seizure disorder, but only 18 of them had received even one of the two flu shots recommended for young children.

But, on the other hand, flu-shot recommendations for young children have changed over the past few years; 76 of the children were in age-groups not specifically recommended to receive flu shots in the years they died.

This flu season, for the first time, federal guidelines call for all children and teens up to 18 to receive flu shots. But motivating parents to get children vaccinated is proving challenging. A recent CDC report said that only about 21% of children 6 to 23 months old were fully vaccinated in the 2006-07 flu season, 2 years after guidelines recommended they be immunized, and a smaller study this year found only 16.5% of 2- to 5-year-olds were fully vaccinated.

Given low levels of vaccine protection, physicians should consider giving influenza antiviral drugs when children are hospitalized with flu, because the drugs have been shown to reduce complications, the article says. And given how rapidly the reported deaths occurred, vancomycin or another antibiotic of last resort should be considered if MRSA is suspected and until it can be ruled out by lab tests.

Finelli L, Fiore A, Dhara R, et al. Influenza-associated pediatric mortality in the United States: increase of Staphylococcus aureus coinfection. Pediatrics 2008;122:805-11 [Abstract]

See also:

Reports on the following topics:

Estimates of children's mortality from flu:
Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 2003;289:179-86 [Abstract]

Influence of pneumococcal vaccines:
Whitney CG, Farley MM, Hadler J, et al.
Decline in invasive pneumococcal disease after the introduction of protein-polysaccharide conjugate vaccine. N Engl J Med 2003;348:1737-46 [Abstract]

Incidence of community-acquired staph pneumonia:
Fine MJ, Smith MA, Carson CA, et al. Prognosis and outcomes of patients with community-acquired pneumonia. A meta-analysis. JAMA 1996;275:134-41 [Abstract]

Bacterial pneumonia and pandemic flu:
Schwarzmann SW, Adler JL, Sullivan RJ, Jr., et al. Bacterial pneumonia during the Hong Kong influenza epidemic of 1968-1969. Arch Intern Med 1971;127:1037-41

1957:

Louria DB, Blumenfeld HL, Ellis JT, et al. Studies on influenza in the pandemic of 1957-1958. II. Pulmonary complications of influenza. J Clin Invest 1959;38:213-65 [Full text]

1918:

Morens DM, Taubenberger JK, Fauci AS. Predominant role of bacterial pneumonia as a cause of death in pandemic influenza: implications for pandemic influenza preparedness. J Infect Dis 2008;198:962-70 [Full text]

MRSA colonization statistics:
Gorwitz RJ, Kruszon-Moran D, McAllister SK, et al. Changes in the prevalence of nasal colonization with Staphylococcus aureus in the United States, 2001-2004. J Infect Dis 2008;197:1226-34 [Full text]

Flu immunization coverage in children:
Sep 26 CIDRAP News story "Flu shots for small children slow to catch on"

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