Detection of Avian Influenza A(H7N2) Virus Infection Among Animal Shelter Workers Using a Novel Serological Approach—New York City, 2016–2017

Abstract

Background.-In 2016, an influenza A(H7N2) virus outbreak occurred in cats in New York City's municipal animal shelters. One human infection was initially detected.Methods.-We conducted a serological survey using a novel approach to rule out cross-reactive antibodies to other seasonal influenza viruses to determine whether additional A(H7N2) human infections had occurred and to assess exposure risk.Results.-Of 121 shelter workers, one had serological evidence of A(H7N2) infection, corresponding to a seroprevalence of 0.8% (95% confidence interval, .02%-4.5%). Five persons exhibited low positive titers to A(H7N2) virus, indicating possible infection; however, we could not exclude cross-reactive antibody responses to seasonal influenza viruses. The remaining 115 persons were seronegative. The seropositive person reported multiple direct cat exposures without using personal protective equipment and mild illness with subjective fever, runny nose, and sore throat.

Identification of novel influenza A virus exposures by an improved high‐throughput multiplex MAGPIX platform and serum adsorption

“…Serum adsorption reduced cross‐reactive binding antibodies and enhanced the difference between the MN ≥40 and MN <40 groups for samples from the A(H7N2) study. The results are consistent with our previous report, and exposed novel HA antigen can be determined more accurately after serum adsorption . On the other hand, no significant difference was achieved for samples from the A(H5N1) study, partly due to the selection of samples that showed either high cross‐reactivity in MFIs against H5.Indo.06 GH after 2‐Ads (>2000) and/or relatively high MN titer against A/duck/Bangladesh/1907/2013 (GMT 23, Table ).…”

“…For example, the age‐related antibody baseline level to A(H1N1)pdm09 in recent years would be much higher than those reported in 2009, due to extensive exposure to A(H1N1)pdm09 virus through infection or vaccination post‐2009 . If we can determine whether low levels of age‐specific, subtype cross‐reactive antibodies are present in the population, single convalescent‐phase serum specimens may be sufficient to determine a recent exposure to novel subtype influenza …”

“…We have previously demonstrated that cross‐reactivity could be reduced by incorporating a serum adsorption step prior to the MAGPIX or MN assays, and the remaining signals from post‐adsorption samples represent HA subtype‐specific responses . Thus, serum adsorptions were performed in the current study to remove cross‐reactive antibodies to improve sensitivity and specificity.…”

“…In the A(H7N2) study, single convalescent serum specimens (S2) were collected from 119 shelter workers and volunteers (18‐73 years, median age 31 years) during an A(H7N2) animal shelter outbreak in New York City in 2016‐2017, and the median days from last exposure to serum collection was 36 days (Table ). One seropositive participant (MN titers ≥40 and HI titers ≥40), 5 indeterminate participants (MN titer ≥40 and HI titer < 40), and 113 seronegative participants (MN < 40 and HI < 40) were identified in the sero‐epidemiology study …”

“…18 In this study, we observed high MFIs against We have previously demonstrated that cross-reactivity could be reduced by incorporating a serum adsorption step prior to the MAGPIX or MN assays, and the remaining signals from post-adsorption samples represent HA subtype-specific responses. 4,7 Thus, serum adsorptions were performed in the current study to remove cross-reactive antibodies to improve sensitivity and specificity. Following the initial analysis, eighteen S2 samples from the H7N2 study that showed either MN ≥40 or MFI >3500 against H7.NY.16 Ecto (H7N2) and 14 samples that showed MFI >1300 against H5.Ind.05 GH (H5N1, clade 2.1.3.2) from H5N1 study were selected for either mock or adsorption using two rHAs (2-Ads) ( Figure 1C, Tables 2 and 3, and Figure S1).…”