{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,31]],"date-time":"2026-10-31T16:22:16Z","timestamp":1793463736203,"version":"4.5.0"},"reference-count":35,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2023,11,22]],"date-time":"2023-11-22T00:00:00Z","timestamp":1700611200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Microbiol."],"abstract":"<jats:sec><jats:title>Introduction<\/jats:title><jats:p>This study aimed to investigate the epidemiology, serotype distribution, phenotypical antibiogram, and molecular resistance gene characteristics of invasive <jats:italic>Haemophilus influenzae<\/jats:italic> infections in Denmark from 2014 to 2022. Additionally, the potential impact of outdoor temperature and COVID-19 restrictions on the epidemiology of <jats:italic>H. influenzae<\/jats:italic> was assessed.<\/jats:p><\/jats:sec><jats:sec><jats:title>Materials and methods<\/jats:title><jats:p>Invasive <jats:italic>H. influenzae<\/jats:italic> isolates were received from patients with positive culture results from cerebrospinal fluid, blood, or other sterile sites. Sample data were obtained from the Danish laboratory surveillance system\/MiBa database, and whole-genome sequencing (WGS) was performed on the isolates. The incidence rates and distribution of <jats:italic>H. influenzae<\/jats:italic> cases were analyzed, and antibiotic susceptibility were assessed.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>A total of 1,007 invasive <jats:italic>H. influenzae<\/jats:italic> cases were identified, with serotyping conducted for 752 (74.7%) isolates. The median incidence per year of <jats:italic>H. influenzae<\/jats:italic> was 2.0 cases per 100,000, with the highest incidence in 2014 and the lowest in 2020. The majority of <jats:italic>H. influenzae<\/jats:italic> isolates were non-typeable <jats:italic>H. influenzae<\/jats:italic> (NTHi), while the most prominent serotypes were serotype f followed by serotype b. Bacteremia cases accounted for the majority (88.6%) of occurrences, although meningitis cases showed an increasing trend during the time period. The age group 85+ exhibited the highest incidence. The implementation of COVID-19 preventive interventions in 2020 resulted in a significant reduction in <jats:italic>H. influenzae<\/jats:italic> incidence, which returned to pre-COVID levels in 2021. A negative correlation was observed between monthly <jats:italic>H. influenzae<\/jats:italic> cases and outdoor temperature. An overall level of genetic beta-lactamase resistance of 26.3% was observed divided into 10.6% beta-lactamase-positive ampicillin-resistant (gBLPAR), 13.6% beta-lactamase-negative ampicillin-resistant (gBLNAR) and 2.1% beta-lactamase-positive amoxicillin clavulanate-resistant (gBLPACR). Other non-beta-lactam resistance traits were detected in 7.6% of isolates (primarily aminoglycoside-modifying enzymes).<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>The overall incidence of <jats:italic>H. influenzae<\/jats:italic> in Denmark returned to stable levels after the COVID-19 epidemic, with NTHi strains dominating. The COVID-19 preventive interventions led to a major reduction in incidence. A significant negative correlation between the incidence of <jats:italic>H. influenzae<\/jats:italic> and temperature was observed. The study revealed an overall genetic beta-lactam resistance rate of 26.3%, and the concordance between genotypic and phenotypic beta-lactam resistance was high (98.2%).<\/jats:p><\/jats:sec>","DOI":"10.3389\/fmicb.2023.1307261","type":"journal-article","created":{"date-parts":[[2023,11,23]],"date-time":"2023-11-23T15:12:48Z","timestamp":1700752368000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":10,"title":["National Danish surveillance of invasive clinical Haemophilus influenzae isolates and their resistance profile"],"prefix":"10.3389","volume":"14","author":[{"given":"Hans-Christian","family":"Slotved","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thor Bech","family":"Johannesen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marc","family":"Stegger","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tine","family":"Dalby","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kurt","family":"Fuursted","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2023,11,22]]},"reference":[{"key":"ref1","doi-asserted-by":"publisher","first-page":"65","DOI":"10.1128\/AAC.00966-09","article-title":"Antimicrobial resistance in Haemophilus influenzae respiratory tract isolates in Korea: results of a nationwide acute respiratory infections surveillance","volume":"54","author":"Bae","year":"2010","journal-title":"Antimicrob. 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