Detection of mild to moderate influenza A/H7N9 infection by China's national sentinel surveillance system for influenza-like illness: case series

Abstract

Objective To characterise the complete case series of influenza A/H7N9 infections as of 27 May 2013, detected by China's national sentinel surveillance system for influenza-like illness. Design Case series.Setting Outpatient clinics and emergency departments of 554 sentinel hospitals across 31 provinces in mainland China.Cases Infected individuals were identified through cross-referencing people who had laboratory confirmed A/H7N9 infection with people detected by the sentinel surveillance system for influenza-like illness, where patients meeting the World Health Organization's definition of influenza-like illness undergo weekly surveillance, and 10-15 nasopharyngeal swabs are collected each week from a subset of patients with influenza-like illness in each hospital for virological testing. We extracted relevant epidemiological data from public health investigations by the Centers for Disease Control and Prevention at the local, provincial, and national level; and clinical and laboratory data from chart review.Main outcome measure Epidemiological, clinical, and laboratory profiles of the case series.Results Of 130 people with laboratory confirmed A/H7N9 infection as of 27 May 2013, five (4%) were detected through the sentinel surveillance system for influenza-like illness. Mean age was 13 years (range 2-26), and none had any underlying medical conditions. Exposure history, geographical location, and timing of symptom onset of these five patients were otherwise similar to the general cohort of laboratory confirmed cases so far. Only two of the five patients needed hospitalisation, and all five had mild or moderate disease with an uneventful course of recovery. ConclusionOur findings support the existence of a "clinical iceberg" phenomenon in influenza A/H7N9 infections, and reinforce the need for vigilance to the diverse presentation that can be associated with A/H7N9 infection. At the public health level, indirect evidence suggests a substantial proportion of mild disease in A/H7N9 infections.

Amino Acid Substitutions in Polymerase Basic Protein 2 Gene Contribute to the Pathogenicity of the Novel A/H7N9 Influenza Virus in Mammalian Hosts

“…Patients with A/H7N9 viruses typically develop a rapidly progressive viral pneumonia leading to respiratory failure and acute respiratory distress syndrome (ARDS), reminiscent of human HPAI H5N1 disease (1,2). There is evidence that infection may also lead to mild or asymptomatic infections, and the true extent of infection is believed to be much greater, resulting in a significant "iceberg" of unrecognized infection (3). Mutations in the viral hemagglutinin allow this H7N9 virus to bind both avian-like and human-like receptors in the human respiratory tract, conferring efficient tropism for the human conducting airways and lungs, thus explaining the relative ease with which this virus crosses species from birds to humans (4)(5)(6).…”

Unique Determinants of Neuraminidase Inhibitor Resistance among N3, N7, and N9 Avian Influenza Viruses

“…Although NAI-resistant mutations have been well studied and profiled in human influenza A viruses of N1 and N2 subtypes and in influenza B viruses, they are poorly understood in avian NA subtypes despite the fact that many avian viruses of the H5, H6, H7, H9, and H10 subtypes and the N1, N2, N3, N7, N8, and N9 subtypes cause human infection (27)(28)(29)(30)(31). NA subtypes are classified into two phylogenetically and structurally distinctive groups: group 1 containing N1, N4, N5, and N8 and group 2 containing N2, N3, N6, N7, and N9 (32,33).…”

Divergent H7 Immunogens Offer Protection from H7N9 Virus Challenge

“…Importantly, the mutations that confer resistance do not impact viral pathogenicity in the mouse model or the ability of the virus to transmit in the guinea pig model (5). Although no sustained human-to-human transmission has been detected so far (6), the ability of the hemagglutinin (HA) of this novel strain to bind weakly to alpha-2,6-linked sialic acid (7)(8)(9)(10)(11) suggests that H7N9 viruses could potentially become transmissible among humans. Subtype H7 viruses do not currently circulate in humans, and thus, any H7 virus that acquires the ability to spread from human to human could, if introduced into a naive population, cause a pandemic.…”