BACKGROUND:
Diphtheria remains a significant public health challenge in Kaduna State, Nigeria, with ongoing transmission across multiple Local Government Areas (LGAs). Despite response efforts, sustained case reporting from Week 1 to Week 42 of 2025 indicates persistent community spread. The outbreak originated from an index case identified in Ikara LGA on 26 December 2024, who presented with classical diphtheria symptoms.

METHODS:
Data were derived from routine Integrated Disease Surveillance and Response (IDSR) reporting, health facility line lists, laboratory records, and outbreak investigation updates. Variables analyzed included the number of suspected and confirmed cases, geographical distribution, mortality outcomes, sample collection, and patient recovery status.

RESULTS:
A total of 852 suspected cases were reported from 16 LGAs between Week 1 and Week 42, 2025 with 232 samples collected, 56 were laboratory confirmed for diphtheria. The highest confirmed burdens were recorded in Sabon Gari (15), Zaria (10), and Kaduna South (8). Week 42 alone recorded 15 new suspected cases from Ikara (1), Giwa (6), and Kudan (8). There were 26 deaths, yielding a case fatality rate (CFR) of 3.1%. Clinical outcomes improved significantly, with 826 recoveries and no active admissions at the time of reporting.

CONCLUSIONS:
The diphtheria outbreak in Kaduna State remains active with evidence of widespread across LGAs. Despite high caseloads, improved clinical management has resulted in high recovery rates with no active case on admission as at the time of reporting. Continued strengthening of surveillance, laboratory capacity, and targeted public health interventions, including vaccination, risk communication and community engagement is essential to stop transmission and prevent further morbidity and mortality.