Commentary
Alarming
Explosion of Mild H5N1 Toddler Cases in Egypt
Recombinomics Commentary
21:25
April 3, 2009
There is no obvious explanation for the explosion in toddler cases this year. In the prior three years there were only six toddler cases, which represented 12% of H5N1 confirmed cases. The frequency in 2009 is almost 10 fold higher. Moreover, since these cases are mild, and are largely limited to those with known poultry links, the number of actual infections is likely much higher.
The large number of cases suggests that the transmission to humans is more efficient, and mild cases are more likely to spread silently. Mild cases will be more likely to be diagnosed as seasonal flu, and those without a known link to poultry are unlikely to be tested. Moreover, the absence of pneumonia in almost all confirmed cases suggests that many other cases would resolve without Tamiflu treatment.
The mild cases in the spring of 2009 have similarities to cases in the spring of 2007, although the target population has changed. In the spring of 2007 the case fatality rate was also close to zero (16/17 survived), but most of the cases were children. That outbreak raised concerns that there were many additional children that were H5N1 infected, but not tested. Milder cases spread more easily because infected hosts remain active longer, increasing the number of exposed contacts, especially when the target population is school aged.
Recovery in the older age groups would lead to protective immunity, which would lower then number of confirmed cases in those age groups. These prior infections would funnel the infections into younger patients who had not been previously exposed.
The 10 fold jump in toddler cases this year raises concerns that undetected cases are also 10 fold higher than prior outbreaks, signaling a major spread of H5N1 in the human population.
The explosion of cases in toddlers demands a more aggressive testing of toddlers that do not have poultry contact. Similarly, an aggressive testing program of former at risk groups for detectable levels of neutralizing antibodies is long overdue.
The explosion of toddler cases strongly suggests that the level of human H5N1 cases in Egypt is markedly higher than the confirmed cases, requiring intensive testing beyond patients with poultry contacts.
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