Photo Credit- CDC
Last January, and for the second year running, we saw just how easily a traveler could carry avian influenza from China to North America when the PHAC issued a Statement On Canada’s first Imported H7N9 Case, followed four days later with the announcement that H7N9 was Confirmed In 2nd B.C. Patient.
Luckily, and in sharp contrast to North America’s first imported H5N1 case (again from a traveler from China), which was reported in January of 2014 (see CDC Statement On 1st H5N1 Case In North America), both H7N9 cases suffered only mild symptoms and fully recovered.
While we have no idea what avian flu might have in mind for an encore this winter, we have the first really detailed report – led by well known Canadian researcher Dr. Danuta M. Skowronski – on these first two H7N9 cases, which appears in the CDC’s EID Journal.
It’s a long, detailed report, and you’ll want to read it in its entirety. When you return, I’ll have some closing thoughts.
Volume 22, Number 1—January 2016
Danuta M. Skowronski , Catharine Chambers, Reka Gustafson, Dale B. Purych, Patrick Tang, Nathalie Bastien, Mel Krajden, and Yan Li
In January 2015, British Columbia, Canada, reported avian influenza A(H7N9) virus infection in 2 travelers returning from China who sought outpatient care for typical influenza-like illness. There was no further spread, but serosurvey findings showed broad population susceptibility to H7N9 virus. Travel history and timely notification are critical to emerging pathogen detection and response.
Since February 2013, >600 human cases of avian influenza A(H7N9) infection have been reported from eastern China, where the virus is considered enzootic in poultry (1). Travel-associated cases have previously been reported in Asia (2); however, in January 2015, Canada reported 2 travel-associated cases, which are described here.
A married couple, both 56 years of age, from British Columbia (BC), Canada, traveled in Hong Kong (December 29, 2014–January 3, 2015, and January 6–7); Taipei, Taiwan (January 3–6); and Fujian Province, China (January 7–11), returning home on January 12. They recalled seeing live poultry and copious droppings while visiting Fujian on January 8 but recollected no other poultry contact.
Around January 3–7, the previously healthy woman experienced mild cough, sore throat, and hoarseness. She recovered, but influenza-like illness (ILI), including fever, cough, myalgia, and fatigue, developed on January 14. On January 15, she sought outpatient care. A healthcare worker (HCW) collected a nasal swab specimen, which was sent to the BC Public Health Microbiology and Reference Laboratory (BC-PHMRL), where most influenza testing is centralized in BC. On January 16, the sample tested positive for influenza A virus by reverse transcription PCR (RT-PCR), and the HCW was informed; the next business day (January 19), the patient was prescribed oseltamivir.
For surveillance purposes, BC-PHMRL conducts subtyping of all detected influenza A viruses. Despite a high virus titer (cycle threshold [Ct] 23.43), the specimen could not be subtyped for human influenza H1 or H3 virus by matrix gene–based RT-PCR. Further subtyping using RT-PCR–based targets for the hemagglutinin gene indicated an H7 virus. Sequence analysis of a matrix gene fragment showed 99% identity with H7N9 and H9N2 viruses, the latter of which is known to have donated internal genes to H7N9 virus (1,3). On January 23, BC-PHMRL notified public health authorities of a presumptive diagnosis of H7N9 virus infection in the woman (index case), and on January 26, Canada’s National Microbiology Laboratory (NML) confirmed the diagnosis by RT-PCR.
On January 13, a day before the woman became ill, her husband, who had a history of asthma, had onset of ILI symptoms (fever, productive cough, chest pain, dyspnea, headache, myalgia, and fatigue) and visited the same HCW. The HCW prescribed doxycycline but did not collect a specimen. On January 19, after his wife received a diagnosis of influenza, the man was prescribed oseltamivir. A throat swab specimen collected from him on January 23 was RT-PCR–positive for influenza A (Ct 29.79). On January 29, NML confirmed H7N9 virus infection.
Neither patient experienced conjunctivitis, which has been reported with H7N7 and H7N3 infections (3,4), and both recovered in self-isolation at home. Follow-up respiratory specimens were still positive by RT-PCR on January 26 (day 12 after ILI onset for the woman [Ct 36.82]; day 13 for the man [Ct 33.80]) and on January 28 (day 15 after ILI onset) for the man (Ct 30.21).
Despite broad susceptibility and instances of household or familial transmission, H7N9 virus has not demonstrated easy person-to-person spread. Poultry exposure remains the major risk factor for human H7N9 infection (2,3,9). Primary prevention messages should emphasize to travelers that they avoid exposure to poultry and uncooked poultry products while visiting affected areas. As illustrated by a prior imported case of avian influenza A(H5N1) virus to Alberta, Canada, however, such exposures may not always be recognized or avoidable (15). Screening should therefore begin with travel history in the 2 weeks before onset of acute respiratory illness. Patients should be encouraged to volunteer recent travel histories, and HCWs should elicit information regarding travel to affected areas. Public health and laboratory partners should be notified of suspect cases, as appropriate, during the diagnostic work-up, so that emerging pathogen screening, risk assessment, and advice can be guided in a timely manner.
Dr. Skowronski is an epidemiologist at the British Columbia Centre for Disease Control, where she is responsible for surveillance, rapid response research, and policy advice related to influenza and other emerging or reemerging respiratory pathogens. Her primary research interests are influenza molecular and immunoepidemiology and influenza vaccine effectiveness and safety evaluation.
Although the `official’ number of H7N9 cases reported in China remains under 700 going into this next flu season, there are credible estimates that suggest the true number of cases may be many times higher than that (see Lancet: Clinical Severity Of Human H7N9 Infection). Perhaps tens of thousands.
As evidenced by this Canadian couple, H7N9 infection can produce a wide spectrum of illness, and it was somewhat serendipitous that they were detected at all. For the most part, only the `sickest of the sick’ in China are ever tested and identified.
Worth noting, the couple only reported tangential poultry contact while in China (`They recalled seeing live poultry and copious droppings while visiting Fujian on January 8’), and while this may not have been the source of infection, with no other known risk exposures, it does speak to the relative ease of acquiring the virus.
The lack of forward transmission of the virus is encouraging, but as study after study has shown, the H7N9 virus is actively evolving, reassorting, and changing its behavior (see EID Journal: H7N9’s Evolution During China’s Third Wave – Guangdong Province).
Simply put, the H7N9 virus we see this winter may not behave as the H7N9 viruses of past winters.
While that doesn’t necessarily point to any particular outcome (the virus could lose biological fitness, instead of gaining it), it is a reminder of the unpredictability of these viruses.
A final note, this study also notes testing on over 1,600 blood samples taken from residents of B.C. shows broad population serosusceptibility to H7N9 virus. In other words, little or no evidence of acquired immunity.