External quality assessment scheme for identification, antimicrobial susceptibility testing and molecular typing of Haemophilus influenzae, 2026

Despite the success of conjugate vaccination against serotype b, invasive Haemophilus influenzae disease continues to pose a challenge to public health in Europe. Surveillance requires not only reliable species identification, but also accurate distinction between capsulated and non-capsulated strains, capsule typing, antimicrobial susceptibility testing (AST) and, increasingly, genomic characterisation.

This external quality assessment (EQA) was organised within the IBDLabNet framework on behalf of the European Centre for Disease Prevention and Control (ECDC) to assess current European Union/European Economic Area (EU/EEA) laboratory capacity for the detection and characterisation of H. influenzae in both non-culture and culture-based settings. The exercise included a shared non-culture panel and an optional H. influenzae culture panel. Samples were shipped in December 2025, the online response form opened in January 2026, and the submission deadline was 15 April 2026. 

A total of 34 EU/EEA laboratories from 24 countries were included in the EU/EEA analysis. All 34 EU/EEA laboratories received the non-culture panel, 32/34 submitted at least one non-culture sample result to the Research Electronic Data Capture (REDCap) platform, and 23 received the H. influenzae culture panel. 

Overall, performance was strong for identification of culture-based species. Correct identification was reported by 22/23 laboratories (95.7%) for H1 and 23/23 (100.0%) for H2. Capsule typing was more variable: 16/23 laboratories (69.6%) correctly reported H1 as non-typeable Haemophilus influenzae (NTHi), and 18/23 (78.3%) correctly identified H2 as Haemophilus influenzae serotype b (Hib). AST uptake was high, with minimum inhibitory concentration (MIC) testing reported by 19/23 laboratories (82.6%) for H1 and 20/23 (87.0%) for H2. The predefined resistance-associated phenotypes were recognised by most laboratories with interpretable results. Whole genome sequencing (WGS) was reported by 12/23 laboratories (52.2%) for H1 and 13/23 (56.5%) for H2. Among the WGS-positive submissions, reporting completeness was highest for sequence type and lower for Life Identification Number code (LINcode) and some additional outputs.

In contrast, non-culture performance was more heterogeneous. NC2, expected to contain Hib, appeared to be a low-signal and more challenging sample. Among laboratories with an interpretable response, 17/31 (54.8%) correctly identified H. influenzae, and only 2/31 (6.5%) correctly identified Hib when expressed against all interpretable responders. For NC6, expected to contain Haemophilus influenzae serotype a (Hia), species identification was higher, at 25/31 (80.6%), but correct capsule typing remained limited overall at 5/31 (16.1%), despite 5/10 (50.0%) correct results among typed submissions. These findings indicate that non-culture molecular detection, and especially capsule typing, are still the main areas for inter-laboratory variability. 

The EQA confirms that participating EU/EEA laboratories have strong capacity for isolate-based H. influenzae identification, high AST uptake and moderate WGS implementation. However, important gaps remain for nonculture detection and capsule typing, particularly for challenging samples and the completeness of usable surveillance outputs. The design of the exercise was appropriate to document current practice, but interpretation should take into account the limited number of H. influenzae samples, the absence of a negative non-culture sample, optional participation in the culture component, reliance on participant modal MICs for comparative AST analysis, restriction of European Committee on Antimicrobial Susceptibility Testing (EUCAST)-based interpretation to selected informative combinations, and the descriptive nature of the WGS analysis. 

Recommended next steps include continued rounds of EQA, targeted feedback to participants, improved collection of methodological information on non-culture workflows, focused training on molecular detection and capsule typing from non-culture material, further standardisation of AST and beta-lactamase reporting, and progressive harmonisation of WGS-derived outputs. These actions would improve the quality and comparability of invasive H. influenzae surveillance data across the EU/EEA.