The first outbreak of neuroinvasive West Nile virus infection in Istanbul area within 2019

Abstract

Turkiye has reported West Nile virus (WNV) infection outbreaks since 2010. The first—and until then only—local human case in Istanbul was recorded in 2017, followed by an outbreak in 2019. Aims: We describe this first known documented outbreak of neuroinvasive WNV (NWNV) infection in the Istanbul region during the summer and autumn of 2019. Study design: Retrospective, multi-center, cohort study. Methods: Between July and September 2019, 16 cases of NWNV infection were hospitalized at six referral hospitals in Istanbul. Additionally, we included one resident case diagnosed and treated at Istanbul School of Medicine Hospital in 2017, representing the first known confirmed—but previously unreported—WNV infection in Istanbul. Results: Among total 17 cases, 14 had meningoencephalitis, two meningitis, and one flaccid paralysis. Median age was 63 years; 65% were male. Most lived in the European part of Istanbul near lakes or dams, but only 24% (4/17) reported recent mosquito exposure. Median symptom duration before admission was 6 (0–24) days. Underlying conditions were present in 82% (14/17), most commonly hypertension (41%), diabetes (35%), chronic kidney disease (CKD) (18%), and onco-hematological diseases (18%). WNV serology (IgM, IgG), plaque reduction neutralization test, PCR, and IgG avidity testing were performed except CSF IgM. There was one in-hospital mortality case with CKD after 76 days of hospitalization. Neurological sequelae occurred in 47% (8/17), including lower limb paresis (n = 3), parkinsonian gait, aphasia, sensorineural hearing loss, respiratory muscle weakness, and retinitis (one each). Conclusion: NWNV infection should be considered as a potential cause of meningoencephalitis in Istanbul, particularly during the summer and autumn months. Patients presenting with gastrointestinal or flu-like symptoms followed by ataxia, dysarthria, slowed speech, tremor, or ocular abnormalities should be tested for WNV infection. Clinical trial number: Not applicable