Madrid (European News) – The World Health Organization (WHO) reports that on September 2, 2023, the Dutch Ministry of Health, Welfare and Sports notified a laboratory-confirmed case of infection with the (v) variant of the virus found in pigs in the Netherlands. Influenza A (H1N1) virus, affected persons have recovered and are not reported to have had any direct contact with pigs.
The case was discovered during routine surveillance for respiratory diseases. According to available information, as of September 7, there were no symptomatic contacts of this case, and no further test reports were found during daily monitoring. Five close contacts were tracked for a maximum incubation period of 10 days, and no one developed symptoms.
Therefore, there is no evidence of human-to-human transmission and the case is considered a sporadic human case of influenza A (H1N1). The potential for human-to-human community transmission and/or international spread of the disease through humans is considered low.
Influenza A (H1) viruses are circulating in swine herds in most parts of the world. When an influenza virus that normally circulates among pigs is detected in humans, it is called an “influenza virus variant.” H1N1, H1N2, and H3N2 are the major subtypes of swine influenza A viruses in pigs that occasionally infect humans, usually after direct or indirect contact with pigs or contaminated environments.
Human infection with the virus variant tends to cause mild clinical illness, although some cases result in hospitalization for more severe disease and others are fatal. Sporadic human infections caused by influenza A (H1N1v) and influenza A (H1N2v) viruses have been previously reported in the Netherlands, but there was no evidence of sustained human-to-human transmission.
This is the first human infection caused by influenza A H1N1 virus reported in the Netherlands in 2023, and the third human infection in the past five years. Nine cases of the human variant have been recorded in the Netherlands since 1986.
Case description and public health response
This was an adult from the province of Noord-Brabant with no underlying medical conditions or history of occupational exposure to animals. On August 20, 2023, the patient developed fatigue and discomfort. He developed acute respiratory infection the next day, with chills, sneezing, coughing, headache and general weakness, and then developed fever on August 22.
On August 21, 2023, as part of participatory surveillance for acute respiratory infection, the patient reported symptoms and had his combined nasopharyngeal swab sample collected sent to the laboratory. On August 22, 2023, the sample was sent to the location of the Dutch National Influenza Center at the National Institute of Public Health and the Environment (RIVM). The test result was positive for influenza A virus and negative for influenza A H1N1. )pdm09, both tests are included in the 24-pathogen multiplex nucleic acid amplification assay commercialized on August 23.
Further routine subtyping by RT-qPCR testing was performed on August 24 and 25. Tests for seasonal influenza virus and H5 virus were negative. Additionally, a laboratory-developed test (LDT) and another commercial universal influenza A virus detection method confirmed the presence of influenza A virus in the sample.
On August 28, routine whole-genome sequencing and virus isolation began using nanopore technology. On August 30, sequencing results showed that virus A/Netherlands/10534/2023 was the Eurasian avian swine influenza A (H1N1) v clade 1C.2.2 virus.
The HA genome fragment clustered closely with recent 2022 and 2023 clade 1C.2.2 swine influenza viruses from the Netherlands. It is less closely classified than the A(H1N1)v (from 2019) and A(H1N2)v (from 2020) viruses of the previous clade 1C.2.2 from the Netherlands. Phenotypically, the virus is sensitive to the neuraminidase inhibitors oseltamivir and zanamivir.
The virus isolate will be shared with the WHO Collaborating Center in London, United Kingdom of Great Britain and Northern Ireland, and the World Organization for Animal Health (WOAH) Animal and Plant Health Agency (APHA) Avian and Swine Influenza Reference Laboratory. U.K. These sequences can be found in the GISAID database under accession number EPI_ISL_18168180.
As of September 13, the patient has recovered. The investigation report states that the individual did not work on a pig farm or any other pig-related business, nor did he work in the health care industry. Therefore, there is currently no clear source of infection.
Regarding the public health response, the WHO explained that national authorities monitored cases and all close contacts. WHO is notified through the European Commission’s confidential Early Warning and Response System (EWS). Currently, further antigen identification of the virus is ongoing. The Zoonoses Center and veterinarians conducted investigations but found no possible source of infection. Therefore, no animal monitoring or testing was performed.
Almost no influenza viruses have been detected in the Netherlands, and apart from the cases reported so far, none are variants of the swine influenza A virus.