Serology study finds H5N1 transmission low, despite close contact
A serologic study of people who were exposed to patients with confirmed H5N1 avian flu in China found evidence of only two asymptomatic infections, suggesting that the virus isn't easily transmissible, researchers reported yesterday.
The team included scientists from the Chinese government, the World Health Organization (WHO), and the US government, and their findings appeared in PLoS One.
The study is based on blood samples and epidemiologic information taken from household contacts and social contacts of 23 of 30 H5N1 patients reported in China from 2005 through 2008. It included 87 household members and 332 social contacts.
Only two (2.3%) of the household contacts tested positive for H5N1 antibodies, and all of the social contacts tested negative. Only three of those studied had direct contact with patients' respiratory or fecal secretions, and all of them tested negative. Among the contacts, 71 had direct contact with an H5N1 patient through bedside care or physical contact.
None of the 419 contacts wore appropriate physical protective equipment when they were exposed to the H5N1 patient during the infectious period, and only 12 said they wore a surgical mask.
The group's review of the epidemiologic data found that 12% of close contacts had been exposed to sick or dead poultry, and 31% had recently visited a live-poultry market. None of the close contacts received oseltamivir (Tamiflu) to prevent H5N1 infection, but close contacts of three patients receive other antivirals.
The two people who tested positive for H5N1 exposure reported no symptoms, and both were blood-related family members.
Researchers concluded that the most likely source of their infections was probably limited, nonsustained human-to-human transmission, which could have occurred through prolonged, unprotected close exposure, such as providing care or sleeping together. However, the group noted that backyard poultry died at the homes of both positive contacts, which raises the possibility that poultry or environmental exposure could have been the source of the virus.
The team concluded that although transmission during that period was low, even with prolonged and unprotected exposure, the virus continues to evolve, making the risk to humans unpredictable.
Aug 13 PLoS One report
Fatal H7N9 cases characterized by bacterial infection, alveolar damage
Fatal H7N9 infections in a case series of 12 intensive care unit (ICU) patients in a hospital in Hangzhou, China, were characterized by secondary bacterial pneumonia, and four of the six patients who died had H7N9 influenza virus in their stool. The study was published yesterday in Clinical Infectious Diseases.
Researchers analyzed viral loads and other data from patients admitted to the ICU from Apr 10 to 23. They also examined postmortem biopsies of the lung, liver, kidney, spleen, bone marrow, and heart from the six patients who died.
They found median viral load in fatal cases to be higher in sputa than in nasopharyngeal swabs. Polymerase chain reaction tests were positive for H7N9 in stool samples in four of the fatal cases and two of the survivors but were negative in the cerebrospinal fluid, urine, and blood of all patients.
Five patients who died had nosocomial bacterial infections, compared with three who survived. Three of those who died had evidence of "acute diffuse alveolar damage" at autopsy, the authors said.
Aug 13 Clin Infect Dis abstract
H7N3 hits another Mexican farm
Agriculture officials in Mexico recently reported another highly pathogenic H7N3 outbreak in poultry, part of the country's ongoing battle against the strain that began in 2012.
An Aug 12 report to the World Organization for Animal Health (OIE) said the virus turned up at a layer farm in Jalisco state, a top egg-producing area in the central part of the country. The farm has 359,343 susceptible birds, and the outbreak there was first detected on Jul 30.
The source of infection is thought to be contact with wild species, according to the report. Control measures that were previously applied at the farm are ongoing, including vaccinating birds and surveillance as part of a national effort.
This latest H7N3 outbreak is Mexico's first since the middle of June, when the same virus struck eight farms in four different states.
Aug 12 OIE report