Rapid identification of imported influenza viruses at Xiamen International Airport via an active surveillance program

Abstract

Objectives: The cross-border transmission of infectious diseases is a worldwide public health issue. Current border screening measures are insufficiently sensitive. The study objectives were to describe the epidemiologic pattern of influenza infection among incoming travellers at Xiamen International Airport during nonpandemic periods and to assess the performance of a rapid influenza diagnostic test in border screening.

Methods: Between May 2015 and May 2016, travellers with influenza-like illnesses entering China at Xiamen International Airport were screened with a rapid test, Flu Dot-ELISA, and the collected specimens were further subjected to virus isolation and phylogenetic analysis.

Results: Of the 1 540 076 incoming travellers, 1224 cases of influenza-like illness were identified; 261 tested positive in the rapid test, and 176 were confirmed to be influenza through virus culture. The sensitivity and specificity of the rapid test were demonstrated to be 96.6% (170/176) and 91.3% (957/1048), respectively, and the positive predictive and negative predictive values were 65.1% (170/261) and 99.4% (957/963), respectively. The epidemiologic study indicated that H3N2 and (H1N1)pdm09 were dominant in 2015 and 2016, respectively. In 2016, an increased number of influenza B isolates and cocirculation of both Victoria and Yamagata lineage influenza B viruses were observed, and mismatches between circulating influenza A(H1N1)pdm09 and influenza B Victoria lineage strains and vaccine strains also occurred.

Conclusions: We demonstrated the suitability and value of a high-sensitivity rapid influenza test in border screening and highlighted the importance of incoming travellers as a source of imported infectious diseases.

Keywords: Border screening; Phylogenetic analysis; Rapid test; Vaccine mismatch; influenza.

Fig. 1

Flowchart of study's active influenza surveillance system process.

Fig. 2

Monthly distribution of influenza viruses isolated from incoming travellers with ILI symptoms at Xiamen International Airport entry border between May 2015 and May 2016. Bars represent number of influenza isolates; plotted line represents number of ILI specimens. Red bars indicate number of influenza isolates; blue bars, number of influenza B isolates. ILI, influenza-like illness.

Fig. 3

Monthly distribution of various influenza virus subtypes/lineages. Bars represent percentage prevalence of isolates obtained each month: Flu A/H1N1 (red), Flu A/H3N2 (yellow), Flu A/untyped (blue), Flu B/Yamagata (green), Flu B/Victoria (purple).

Fig. 4

Phylogenetic trees of HA genes of representative influenza viruses isolated in this study. (A) Phylogenetic tree of HA genes of influenza A(H1N1)pdm09 isolates. (B) Phylogenetic tree of haemagglutinin (HA) genes of influenza A(H3N2) isolates. (C) Phylogenetic tree of HA genes of influenza B isolates. Virus names in pink represent strains isolated during 2015; virus names in blue represent strains isolated during 2016. Virus names in red and accompanied by solid red circle indicate influenza vaccine strains recommended by World Health Organization. Virus names in black indicate reference strains representing various subclades and sublineages. Vaccine and reference strain HA sequences were downloaded from GenBank. Data were analysed with MEGA 5.2 software, and maximum likelihood methods were used, with 1000 bootstrap replicates. Subclade or sublineage of each virus is classified according to reference strains that they cluster with.