Monday, August 03, 2015

JMII: Epidemiology Of Human Influenza A(H7N9) Infection In Hong Kong





Since the H7N9 virus emerged in Mainland China in the spring of 2013, sparking the first of three mini-epidemics, 13 cases have turned up in Hong Kong.  All are considered imported cases, as all had recent travel to the mainland, and no secondary infections among their contacts have been reported.


Ten of these cases were imported during the 2013-14 winter season, and today we’ve got a detailed epidemiological report on them from researchers at Hong Kong’s Centre for Health Protection.


The full text of the report is available (online or in PDF format), and is well worth reading it its entirety, as it sheds additional light on the demographics, symptomology, incubation period, duration of viral shedding, and effects of antiviral treatment with H7N9 cases.


First a brief excerpt from the abstract with appears in the Journal of Microbiology, Immunology and Infection (JMII), after which I’ll return with a bit more regarding one of their conclusions.


Epidemiology of human influenza A(H7N9) infection in Hong Kong

Yiu-hong Leung, May-kei To, Tsz-sum Lam , Shui-wah Yau, Oi-shan Leung, Shuk-kwan Chuang

Centre for Health Protection, Department of Health, Hong Kong, China

Published Online: July 25, 2015



A total of 10 cases were reported and all were imported infection from Mainland China. Four patients died and the cause of death was related to influenza A(H7N9) infection in two patients. The median interval from illness onset to initiation of oseltamivir treatment for the severe cases (4.5 days) was significantly longer than the mild cases (2 days; p = 0.025). Severe cases had a significantly longer viral shedding duration than mild cases (p = 0.028). The median incubation period for cases with a single known exposure date was 4 days. Nasopharyngeal aspirate taken from the 88 close contacts of the 10 patients all tested negative for influenza A virus using reverse transcription polymerase chain reaction.


Delayed administration of antiviral treatment may be associated with a more severe illness for influenza A(H7N9) infection. Despite our aggressive contact tracing policy with laboratory testing of all close contacts, no secondary case was identified which implied that the potential of human-to-human transmission of the circulating influenza A(H7N9) virus remains low.

(Continue . . . )


Although based on a limited number of cases (n=10), this study adds a bit more  to the growing body of evidence that the early administration of antivirals can help reduce morbidity and mortality in cases of severe influenza.


While that won’t come as much of a surprise to most medical experts, given demonization that antivirals have received online and in the `popular press’ over the past few years,  it is worth highlighting.


Much of the ire surrounding these drugs has been due to Roche’s long-standing resistance to releasing all of their testing data, and that has led to critical editorials in the BMJ, and frequent excoriation in the British press  (see Daily Mail: Ministers blew £650MILLION on useless anti-flu drugs)..


As a result of this sort of hyperbolic coverage, many people have come away with the erroneous impression that these drugs are worthless – or worse.


While its benefits may be limited in mild influenza in healthy adults, we’ve seen numerous observational studies that show antivirals are useful in the treatment of severe flu (see Study: Antivirals Saved Lives Of Pregnant Women  and  Study: The Benefits Of Antiviral Therapy During the 2009 Pandemic), particularly in those with heightened risk factors.  


And even more impressively (and perhaps, more importantly with avian flu viruses on the rise again), in 2010’s Study: Antiviral Therapy For H5N1, a study of outcomes of H5N1 patients who either received, or did not receive, antiviral treatment found:


Out of 308 cases studied, the overall survival rate was a dismal 43.5%.  But . . . of those who received at least one dose of Tamiflu . . .  60% survived . . .  as opposed to only 24% who received no antivirals.


Evidence which helps explain why, we’ve seen a push back by many public health agencies (see The CDC Responds To The Cochrane Tamiflu Study & UK PHE’s  Revisiting Influenza Antiviral Recommendations), strongly recommending the early administration of antivirals in cases of severe flu or in patients with elevated risk factors.


While far from perfect, and not a `cure’ for flu, antivirals remain our best pharmaceutical option for the treatment of severe influenza.

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