The European Center for Disease Prevention and Control (ECDC) has released official information in its bulletin for week 5 of this year (January 28-February 3) about the first known case this year in worldwide of infection with the swine flu virus (A(H1N1) in a human. The contagion was notified to this European Union agency by the health authorities of Spain on January 29 and corresponds to a worker on a farm in the province of Lleida who, after presenting unusual flu symptoms, was detected infected with the A(H1N1) virus, whose variant in humans is technically called A(H1N1)v.
The affected person presented the first symptoms of the viral infection at the end of November and requested medical assistance three times in three weeks, receiving an initial diagnosis of bronchitis, with no signs of pneumonia. On December 12, one of the clinical analyzes of the samples collected from this patient tested positive for influenza or influenza type A (different from the usual seasonal flu at that time in much of Catalonia and the rest of Spain). Subsequent analyzes in Catalonia and at the National Institute of Microbiology confirmed that it was specifically an infection by the swine flu virus A(H1N1).
The ECDC has indicated that, according to the information received from the Spanish health authorities, after the detection of this case, surveillance (tracing) was carried out for other possible similar infections in the area, with no other cases detected to date. The sick worker has recovered satisfactorily, according to the data received by the European authority. This newspaper has requested more information about this case from the Department of Health of the Generalitat of Catalonia and the Ministry of Health, competent authorities that to date (11 a.m. on February 6) have not published (according to the data consulted by this newspaper and, except for error or omission) no communication in this regard through any of the usual public information channels.
Curiously, the Public Health Alerts bulletin of the Ministry of Health of the Community of Madrid published information about this case detected in Catalonia in its edition dated February 2. Reference to this infection detected in Catalonia can also be found in the Cidrap health alert system of the University of Minnesota (United States).
The note published in the ECDC bulletin, the only official public communication of the case known so far, specifically indicates the following:
“On January 29, 2024, the Spanish authorities notified a possible case of human infection with swine flu. Variant of the A(H1N1) virus (A(H1N1)v) in an adult worker on a pig farm. The patient has no history of underlying disease. He lives in Catalonia and has developed symptoms (cough with mucopurulent expectoration, fever, malaise and myalgia). On November 25, 2023 he contacted an outpatient clinic three times in three weeks from the onset of symptoms. There were no signs of pneumonia after the chest x-ray and he was diagnosed with bronchitis.”
On December 12, 2023, a nasal and oropharyngeal swab sample tested positive for influenza A, which could not be subtyped. It was further analyzed at the regional reference laboratory of Catalonia and was identified as swine influenza A(H1N1)v.
The sample was sent for confirmation to the National Microbiology Institute and the isolated virus will be shared with the WHO Collaborating Center.
The patient has recovered completely. To date, no new cases have been detected among close contacts (family) or among co-workers on the farm through the epidemiological investigation of this case, which, according to the Spanish authorities, is considered closed.
After the analysis of the sequences available in Gisaid (isolation ID: EPI_ISL_18782577), under evaluation at the ECDC and in expert reports, it is concluded that all the genes of the case studied coincide with the swine viruses that are currently circulating.
In total, and since 2011, 73 cases of A(H1N1)v infection have been reported worldwide, coming from Brazil (2), Canada (1), China (42), Denmark (2), Germany (5). , Italy (1), the Netherlands (6), Spain (2), Switzerland (3) and the United States (9). In 2023 (by year of diagnosis or onset), six cases of A(H1N1)v were reported, including two cases detected in EU/EEA countries: Spain (1) and the Netherlands (1). The previous case was reported in Spain with a start date in 2022.
Sporadic transmission of influenza viruses of swine origin to humans has been observed, causing mild to severe infections. reported in several countries, including those in the EU and EEA. Swine influenza viruses circulate widely in the pig population, and direct human exposure to pigs represents the most common risk factor for infection. Therefore, this case of A(H1N1)v in Spain is not unexpected. Cases have also occurred among otherwise healthy people and sporadic infections cannot be excluded when people have direct unprotected contact with infected animals.
When a human infection is detected, contact tracing is necessary to exclude post-contact transmission and implement control measures to prevent human-to-human transmission. Zoonotic influenza viruses isolated from patients should be sequenced and further characterized, as well as shared with the national influenza service, reference laboratories and WHO collaborating centres.
The general risk of spread of this type of flu is very low for the general population and low for the workplace. Sporadic cases can be expected.
ECDC published testing and detection of zoonotic influenza virus infections in humans in the EU and EEA, as well as occupational health and safety measures for people exposed at work, in October 2022, and a report of threat assessment on Eurasian avian type swine influenza A(H1N1) viruses in July 2020.
