Clinical and epidemiological features of the 2019 West Nile fever outbreak in the city of Krasnodar

Background: West Nile fever (WNF) is an emerging infectious disease in the Krasnodar region with understudied clinical and epidemiological manifestations. The role of the urban environment in the formation of new endemic foci remains an open question.

Aim: To characterize the main clinical and epidemiological manifestations of WNF and identify potential foci locations within the city of Krasnodar, using the 2019 outbreak as an example.

Materials and methods: A retrospective analysis was conducted on 78 inpatient medical records of patients diagnosed with WNF in 2019, confirmed via enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). Inclusion criteria required patients to have resided within Krasnodar or its suburbs for at least one month prior to symptom onset. Using the online resource Yandex.Maps, we recorded the actual residential addresses of the cases and created a map to identify potential epidemic foci within Krasnodar and adjacent areas.

Results: The 2019 WNF outbreak in Krasnodar region registered between July and September, peaking in August. The mapping of cases in Krasnodar revealed an association with urban water bodies, both natural (lakes, ponds) and artificial (reservoirs, abandoned water bodies), with a lesser degree of association with the Kuban river. In the structure of clinical forms of WNF, the meningeal and meningoencephalitic forms predominated (77.4%, Group 1), while the influenza-like form was observed in 25.6% (Group 2). There were no gender differences between the groups; the mean age was 44.7±0.51 years, with 65% being unemployed or retired. Comorbid conditions were present in 84.5% of Group 1 patients and 35.0% of Group 2 patients, with cardiovascular diseases being the most common (46.1%). Group 1 was characterized by an acute onset with febrile fever, general cerebral and meningeal symptoms, ataxia, and meningitis with moderate lymphocytic pleocytosis. In Group 2, 50% of cases began with low-grade fever, with rash (65%), lymphadenopathy (40%), hyperemia and granular pharyngeal mucosa (75%–50%), and cough (30%) being more frequently observed.

Conclusions: Mapping of potential infection sites confirmed the importance of urban water bodies and helped identify areas at risk of WNF transmission. Effective WNF prevention in urban environments requires comprehensive surveillance of water bodies, mosquito control, and monitoring of migratory birds. For timely diagnosis, PCR and ELISA testing for West Nile fever markers should be included in the comprehensive diagnostic evaluation of patients presenting with symptoms of meningitis, meningoencephalitis, or fever of unknown origin with catarrhal symptoms, rash, and lymphadenopathy during the summer-autumn period in the southern regions of Russia.