# 7041
This week the World Health Organization’s Weekly Epidemiological Record (WER) is devoted to a review of human infections by novel (swine & avian) flu viruses over the course of 2012.
The bulk of this epidemiological analysis focuses on the 32 lab-confirmed H5N1 cases reported last year, but attention is also paid to a pair of H7N3 last year in Mexico, and a spate of swine H1N1v, H1N2v, and H3N2v (variant) infections across North America, as well.
The full report is called:
Update on human cases of influenza at the human–animal interface, 2012
This report describes the epidemiology of the 32 laboratory-confirmed human infections with highly pathogenic avian influenza (H5N1) virus that were reported to WHO from 6 countries during 2012, and summarizes the information on other zoonotic influenza infections – A(H3N2) variant, A(H1N1), A(H1N2) and A(H7N3) – reported in 2012 in humans.
Some highlights follow regarding the H5N1 virus (slightly reparagraphed for readability):
The epidemiological curve of human cases follows the same seasonal pattern seen in previous years, with larger numbers of cases in the months December to March (Figure 1). This curve follows the seasonal curve of reported outbreaks in poultry. Of the human cases for the year, 72% (23/32 cases) were reported in the first 3 months of 2012 (1 January to 31 March).
Distribution by age and sex
In 2012, most cases occurred in children and young adults; 90% (29/32) were in people aged <40 years and 34% (11/32) in children aged <10 years. Cases ranged in age from 6 months to 45 years, with a median age of 18 years.
The median age of reported cases has varied annually since 2009: 5 years of age in 2009, 25 years in 2010 and 13 years in 2011. The median age of cases in Egypt remained high for the third consecutive year.
The median age in Egypt in 2009 was 3 years but rose to 27 years in 2010 and 21 years in 2011 and continued to increase in 2012 to 31 years. In 2012, Egypt reported fewer cases of H5N1 infection (11 cases) compared with previous years (39 cases in 2011, 29 cases in 2010, 39 cases in 2009).
In the past few years, the trend in Indonesia has been towards progressively younger cases. In 2012, the median age was 12 years, up from 8 years in 2011, but considerably down from 34 years in 2010 and 20 for 2005–2011. Indonesia also reported a relatively low number of human cases in 2012: 9 cases were reported in 2012, 12 cases in 2011, 9 cases in 2010 and 21 cases in 2009, compared with 55 cases reported in 2006.
In 2012, equal numbers of male and female cases were reported overall, although this pattern was not uniform across countries or age groups. The sex difference was most prominent in Egypt where 82% (9/11) of cases were female. Data from all cases reported during 2003– 2012 show a similar 1:1.2 male:female ratio.
Clinical outcome
In 2012, the overall proportion of fatal cases among
those reported was 62.5% (20/32), slightly higher thanin the previous 3 years (55% in 2011, 50% in 2010, 44% in 2009) but similar to the average of all cases reported to WHO since 2003 (59% [360/610]). The proportion of confirmed cases with fatal outcomes varied among countries and age groups. The proportion of fatal cases among those reported was 100% in Indonesia (9/9) and Cambodia (3/3), and 0 (0/3) in Bangladesh. Considerable differences were also found across age groups.
While the number of confirmed human infections with the H5N1 virus have declined over the past several years, this report cautions:
Although the proportion of reported fatal human cases remains high, the finding of 3 human cases in 2012 with mild infection reinforces concerns that many milder cases of infection occur undetected. Recent reviews of H5 seroprevalence studies found little evidence that large numbers of cases of H5N1 infection are missed.12, 13
However, because of the variation in protocols and standards in the serological studies, as well as persistent questions about serological responses in exposed or infected humans, the frequency of subclinical infection or mild illness remains uncertain.
It is also likely that some severe and fatal cases were not diagnosed and thus missed.
The risks posed by the H5N1 virus, along with other emerging influenza viruses, remains very real. In the discussion portion of this report, the authors write:
Influenza viruses are unpredictable. Their constant evolving nature raises concerns that these viruses could adapt or reassort with other influenza viruses, thereby gaining potential to become more transmissible to or more pathogenic in humans.
Continued monitoring of the occurrence of human infections with non-seasonal influenza viruses and ongoing characterization of the viruses to assess their pandemic risk are therefore critically important for public health.
Close collaboration with animal health partners allows information regarding viruses circulating in animal populations and human populations worldwide to be shared to improve assessment of global influenza risks to health.
WHO continues to stress the importance of global
monitoring of influenza viruses and recommends all
Member States to strengthen routine influenza surveillance. All human infections with non-seasonal influenza viruses should be reported to WHO under the International Health Regulations (2005).
