For epidemiology researchers, it’s the mystery of the summer. So what happened in Missouri, the American state where, on August 22, the first person infected with H5N1 avian flu without any proven contact with a sick animal in the United States was hospitalized? While an epizootic – that is to say an epidemic affecting animals – has been raging for six months among dairy cow herds on American farms, thirteen people had been contaminated by this H5N1 virus, including four agricultural workers in contact with sick dairy cows – a world first – and nine people working on poultry farms. This new case raises the threat of possible contamination between humans, which would be the first step towards a possible pandemic.
The stakes are therefore high, but the first elements which have filtered out, for more than a month, from the epidemiological investigation surrounding this case are rare and fragmentary, communicated by a bulletin posted online every Friday on the site Internet from the US government agency the Centers for Disease Control (CDC).
Over the last three weeks, we successively learned of the contamination of this person, the fact that someone sharing their accommodation had developed flu symptoms at the same time – but had not been tested; that a caregiver who took care of the first case had also fallen ill, but presented a negative PCR test for influenza, and finally that five other caregivers had developed mild respiratory symptoms without carrying out a test.
Incomplete data
These first reports from the field of what constitutes one of the most followed epidemiological surveys in the world are surprisingly incomplete. “Is this just a problem in the way American health authorities communicate or a real lack of responsiveness? »asks Thierry Lefrançois, veterinarian at the Center for International Cooperation in Agricultural Research for Development. “The wording used surprises me, as if there were no public health measures taken”adds the specialist, who, despite belonging to the health risk monitoring and anticipation committee, is unable to obtain more information from the CDC.
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In its bulletin of September 27, the American government health agency specifies that blood samples were taken from the five caregivers who had not carried out a PCR test in order to carry out serologies, tests consisting of looking for the presence of Antibodies specific to an influenza infection, which would act as witnesses to a past infection. Test results from the positive case have been pending for weeks. “This type of analysis takes a day at most, one might wonder why it doesn’t progress more quickly”underlines Thierry Lefrançois, who specifies that a negative test is not sufficient proof of the absence of infection. Logically, the serology of all close contacts should be examined, including those who have not reported any symptoms.
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