Commentary
H5N1
Toddler Demographic in Egypt Increases Concerns
Recombinomics Commentary
14:27
April 2, 2009
However, this year there has only been one confirmed adult case (38F), who quickly recovered and was only symptomatic for four days. The other nine cases were toddlers between the ages of 1 ½ and 2 ½, which has not been previously reported. In the 51 confirmed cases between 2006 and 2008, there were only 6 toddlers and the rate for each year was close to 10%. In contrast, the toddler rate for 2009 has jumped to 90% and most of these cases have been mild and were widely distributed (see updated map).
This changing demographic is not due to a dramatic change in poultry cases. Although the reports to OIE have become less frequent because Egypt had declared endemic H5N1 which only requires reports every 6 months. However, local detailed reports of poultry H5N1 outbreaks indicate that new outbreaks are confirmed almost daily. These outbreaks are largely backyard flocks and include birds that have and have not been vaccinated. H5N1 deaths in small flocks may be discarded or eaten and not reported, so the exposure to H5N1 in birds is markedly higher than confirmed outbreaks.
However, in spite of this high exposure in 2009, there have been no confirmed teenagers or young adult H5N1 cases. Similarly, in the spring of 2007 there was a spike in cases, but most of those patients were children. Those cases were also mild, raising concerns that the number of H5N1 was markedly higher than reported, because most cases would present as seasonal flu. Similarly, H5N1 testing was largely limited to patients who had a history of contact with poultry, which would lead to silent human to human transmission of mild cases. In 2009, there also have been no confirmed cases in children. The oldest non-adult was 2 ½.
This new demographic, which largely limits confirmed cases to toddlers, raises concerns that prior outbreaks were linked to a significant exposure of these earlier populations to H5N1, leading to protective immunity which limited confirmed cases.
In contrast, the toddlers would not have had exposure to the earlier outbreaks and therefore would lack the protective immunity.
Further analysis of this new demographic would be useful. If the lack of confirmed cases in female teenagers or young adults is due to protective immunity, this group should have low levels of H5N1 antibodies.
A comprehensive screening of this demographic would be useful.
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