It added that there is presently no evidence of sustained person-to-person transmission of the virus and the risk of contracting infection in the UK remains very low.
"WHO urges all Member States to remain vigilant and enhance surveillance to detect any early sign that the virus has changed and has attained the possibilities of causing sustained person-to-person transmission," the statement read.
Recognizing this, polio researchers divide vaccine-derived poliovirus (VDPV) isolates into three categories: (a) iVDPVs derived from immunodeficient patients, (b) cVDVPs that show evidence of sustained person-to-person transmission, and (c) aVDPVs from non-immunodeficient patients or environmental sources that are not associated with an outbreak (Kew et al. 2005).
Racing to keep up with swine flu's spread, health agencies warned this morning that the number infected is changing hourly, and the World Health Organization is eyeing an upgrade to pandemic level 5 if it sees sustained person-to-person transmission in at least two countries.
Nonetheless, sustained person-to-person transmission was sufficient to result in a sizeable outbreak, and death was clearly not uncommon.
Although situations involving consecutive human transmission events have been documented (13 ), none of the known clusters have led to sustained person-to-person transmission in the general population.
While a small number (45) of antiviral-resistant cases were reported, 6 there was no evidence of sustained person-to-person transmission of antiviral-resistant strains in the UK despite extensive testing and monitoring.
Human infections with novel or non-human influenza viruses (also known as zoonotic influenza viruses) are rare but can result in a pandemic if sustained person-to-person transmission occurs and the population has little or no pre-existing population immunity to the virus.
This is based on the idea that schools provide an ideal context for spread of infectious diseases because children are more susceptible to infection, less likely to adopt behavioral changes that reduce disease spread, and more likely to sustain person-to-person contact for lengthy periods.
In a multivariable analysis, the following risk factors were independently associated with the development of IFIs: blast injuries sustained while person was on foot patrol (dismounted), traumatic above-knee amputations, and super-massive (>20 units) transfusions of packed red blood cells during the first 24 hours after injury (14 ).
