Nov 29, 2011 (CIDRAP News) – New details about the three most recent human infections with a novel swine-origin influenza virus have emerged over the past few days, along with a preliminary report of similar viruses in a few pigs.
In addition, the European Centre for Disease Prevention and Control (ECDC) today issued a risk assessment for the new virus, saying the threat to Europe is low, though the events underscore the need for better influenza surveillance in both pigs and humans.
The US Centers for Disease Control and Prevention (CDC) reported details about the recent cases in three Iowa children, along with their contacts with each other, in a recent Morbidity and Mortality Weekly Report (MMWR) dispatch. The World Health Organization (WHO) reported additional details about the patients in a Nov 24 statement.
Earlier this year, seven similar but isolated infections were reported in Indiana, Maine, and Pennsylvania.
All three Iowa children were infected with a swine-origin triple-reassortant H3N2 (S-OtrH3N2) that includes the matrix gene from the 2009 H1N1 virus. Of the 10 cases that have been reported in the United States this year, the three Iowa cases are the most recent and the first known to involve limited human-to-human spread.
The first child, a girl, got sick during the second week of November. Three days later, she was seen by her healthcare provider, who obtained a respiratory sample and conducted a rapid diagnostic test, according to the CDC. Based on surveillance routines, the provider forwarded the sample to the University of Iowa Hygienic Laboratory. Her brother had a flu-like illness one day before she did, and her father had one 2 days after he had contact with her, but neither was tested for flu.
None of the family members reported exposure to pigs, though the girl who tested positive had attended a small gathering with other children the day she got sick.
The other two children are brothers who got sick 1 and 2 days after they were exposed to the young girl. Both were seen by a healthcare provider 2 days after the first brother got sick. Their positive influenza samples were forwarded to the state health lab. The boy's mother said no other family members had been sick, and none had been exposed to pigs before the first boy got sick.
An investigation by Iowa health officials found that the two families had not traveled recently or attended any community events. No other illnesses or swine exposures were identified in the adults or children who were in the setting where the kids were exposed to each other. The WHO said the children were exposed to each other at a daycare site and listed their ages as 11 months, 2 years, and 3 years. It added that none of the children were hospitalized and that all three have recovered.
Iowa has enhanced its surveillance for flu-like illnesses in the communities where the patients live and has asked health providers who treat patients with suspected flu to obtain samples and forward them to the state health lab.
The CDC said its complete genome sequencing confirmed that all three specimens were S-OtrH3N2 viruses that had the M gene from the 2009 H1N1 virus. It said little is known about the virus's ability to transmit between humans and from swine to humans, because of the unusual gene combination.
So far there is no sign of ongoing human-to-human transmission, the CDC said, though the situation bears watching, in case the novel virus gains the ability to spread more easily. It urged clinicians to consider swine-origin influenza in people with febrile respiratory illnesses who have had contact with pigs. It added that enhanced surveillance is under way in Iowa and surrounding states.
Similar viruses found in pigs
Meanwhile, an official from the US Department of Agriculture (USDA) told CIDRAP News that the novel virus is one of many reassortant H3N2 viruses that have been identified in swine surveillance. Influenza is common in pigs and typically causes only minor clinical symptoms, so finding positive samples isn't uncommon.
An informal analysis by the USDA's Agricultural Research Service has found that 8 of about 30 swine H3N2 viruses in the GenBank database have the pandemic H1N1 matrix gene so far, said the USDA official, who requested anonymity. "More detailed analyses of these and other samples continue," the official added.
The official said ongoing voluntary swine flu surveillance efforts are significant, so no special activities are under way to test for the novel virus in pigs. Characterization of swine influenza viruses is continuing at the USDA through the National Veterinary Services Laboratories and the National Animal Health Laboratory Network. The work helps health officials better understand emerging influenza viruses, make them available for research, and select isolates for reagents, diagnostic assays, and vaccine seed strains.
Swine producers and their veterinarians voluntarily submit samples into the swine influenza virus surveillance system, which records the data anonymously, except for the state where the sample was collected, according to the official. Newly sequenced samples are submitted to GenBank.
The CDC noted in a Nov 22 statement that several states had reported the novel virus, but it didn't identify the states.
ECDC rates threat as low
The ECDC, in its risk assessment today, said flu surveillance in pigs is weak in both North America and Europe, given that the disease has few implications for food production and safety, and that monitoring infections in swine workers in Europe is particularly weak. The agency said the detections in the United States build an argument for stronger virologic surveillance in both pigs in humans on both continents, along with more formal pandemic potential assessments of emerging viruses.
Since there are no reports elsewhere in the Americas of unexplained flu infections, as there were during the 2009 H1N1 pandemic, the novel H3N2 infections in the US probably don't signal a larger outbreak, the ECDC said, commenting, "The immediate direct threat to human health in Europe is low."
An analysis of the virus in Europe and at some WHO collaborating centers suggests that the H3N2 component of the current seasonal flu vaccine probably won't protect against the novel virus, though people who have been vaccinated in the past with similar H3N2 strains might have some protection, the ECDC said.
Only five human swine-origin flu infections have been reported in Europe in recent years, the agency said. All involved swine-origin H1N1 strains known to circulate in the region's pig herds, it said.
Nov 23 MMWR report
Nov 24 WHO statement
Nov 29 ECDC risk assessment