COMMENTARY

Literature Commentary by Dr. John G. Bartlett: Respiratory Infections, December 2007

Author: John G. Bartlett, MD

Disclosures

January 04, 2008

Influenza

Centers for Disease Control and Prevention (CDC). Update: Influenza Activity - United States and Worldwide, 2006-07 Season, and Composition of the 2007-08 Influenza Vaccine. MMWR Morb Mortal Wkly Rep. 2007;56:789-794. The following summarizes highlights of the report for influenza, 2006-07.

Viral surveillance: As shown in Table 1 , the US Virus Surveillance System found a predominance of influenza A (H1) during most of the 2006-07 season.

Influenza Season: The number of specimens testing positive exceeded 10% for the first time during the week ending December 23, 2006. It was at 28% in the week ending February 10 (Week 6) and then decreased to less than 10% of specimens testing positive at the week ending April 28, 2007 (Week 17). This 14-week season is similar to the 3 prior seasons, which lasted 13-17 weeks.

Composition of the 2007-08 Vaccine: The trivalent influenza vaccine will contain A/Solomon Islands/3/2006-like (H1N1), A/Wisconsin/67/2005-like (H3N2) and B/Malaysia/2506/2004-like viruses. Note that the only change is for the influenza A (H1N1) component, which now has A/Solomon Islands/3/2006; this is an antigenic variant of the H1N1 component of the 2006-07 strain: A/New Caledonia/20/99.

Pneumonia and Influenza-Related Mortality: During the 2006-07 influenza season, the percentage of deaths attributed to pneumonia and influenza did not exceed the epidemic threshold. The highest peak was a 7.7% increase during the week ending February 24, 2007 (Week 8). During the previous 3 seasons, the peaks had been 7.8% to 10.4%.

Influenza-Associated Pediatric Mortality: There were 68 deaths attributed to influenza in persons younger than 18 years of age. Of 53 individuals older than 6 months with a known vaccination status, 50 (94%) had not been vaccinated. Of the 68 deaths, 21 had coinfection with methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-sensitive Staphylococcus aureus (MSSA).

Human Infections With Avian Influenza A (H5N1) Viruses: From December 1, 2003 through July 25, 2007, there were a total of 319 human cases of avian influenza A (H5N1) reported to the World Health Organization (WHO), of which 192 (60%) were fatal. Of the 319 cases, 279 (87%) were in Asia and 13% were in Africa, primarily Egypt. Details are shown in Table 2 .

Comment: The influenza season for 2006-07 was quite mild; in fact, it did not reach the epidemic threshold. This is the second consecutive year of relatively low activity. The surprise was the predominance of H1N1 since H3N2 has been the predominant strain for most of the past decade. It is noted that the H1N1 strain recovered did not match well with the vaccine strain, and this accounts for the only change in the vaccine preparation for the trivalent vaccine to be used in the next influenza season. With regard to avian influenza, the good news is that it has been contained within Asia and Africa; the bad news is that it persists in terms of both the numbers and the 60% mortality rate. The data for sequential years is fairly alarming, although it appears that, at least to date, the total reported cases for 2007 has stabilized when compared to 2006.

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