Introduction

The National Reference Laboratory for Meningococci and H. influenzae (NRZMHi) carries out laboratory surveillance of invasive H. influenzae (Hi) in Germany. The year 2023 was the first post COVID-19 pandemic year, which led to an epidemiology similar to pre-pandemic years.

Materials and Methods

The aim was to present epidemiological data of invasive H. influenzae infections from 2023. Isolates from blood and cerebrospinal fluid (CSF) are considered invasive and must be reported in Germany, but submission to the NRZMHi is voluntary. The NRZMHi performed species confirmation, serotyping and susceptibility testing for ampicillin and cefotaxime on all submitted isolates.

Results

In 2023, invasive Hi were confirmed in 1317 cases; 1274 isolates were from blood, 38 from CSF only. Laboratory surveillance coverage was estimated 80% by comparing NRZMHi submissions with notified cases at the RKI. Most cases were caused by nontypeable H. influenzae (NTHi, 1150 isolates 87.3%), followed by Hif as the most common capsular serotype (90 cases; 6.8%). Hia, Hib, and Hie were at a comparable level with 25 cases (1.9%) for Hia, 24 cases (1.8%) for Hib, and 28 cases for Hie (2.1%). Thus, Hia was found more frequently than in previous years.Hic and Hid were not found in 2023.Among the analyzed cases, patients aged > 40 years were most affected (1136 cases; 88.6% of all cases). Ampicillin susceptibility testing revealed that 325 (20.1%) isolates were ampicillin-resistant (MIC > 1 µg/mL) and 212 (16.3%) showed β-lactamase production.

Discussion

The epidemiology of invasive Hi infections in Germany 2023 was comparable to pre-pandemic years, in particular 2019, when case numbers were 955. As previously, NTHi in elderly patients dominated the cases. The increasing trend of Hia cases and augmenting rates of ampicillin resistance need to be further monitored.