Beginning in June 2017, numerous dengue virus (DENV) infections occurred in the Jining City of Shandong Province, formerly a dengue-free region in East China. We sought to describe the clinical and epidemiological features of this outbreak.

We reviewed the clinical records and epidemiological data regarding a case series of patients diagnosed with DENV in Jining City, from June 30 to September 14, 2017. Diagnosis was confirmed by molecular method, culture, or rapid diagnostic tests. Sequencing of the DENV envelope gene or the whole viral genome was performed for 11 patients. Additionally, neutralizing antibodies against DENV was measured among patients and residents from their same villages.

Data from 150 patients were evaluated in this outbreak. None were diagnosed with dengue hemorrhagic fever or dengue shock syndrome. The patients’ ages ranged between 2–88 years (median 51 years, [IQR=37.5–64.3]), and 100 (66.7%) were female. Epidemiological analyses implicated a man who had visited Saudi Arabia as the likely source of the outbreak. Phylogenetic studies identified DENV serotype 1. Most of the patients demonstrated increases of neutralizing antibody titers one year after infection compared with titers three months after infection. The residents living in dengue-affected villages had a significant higher seroprevalence of 21.2% (95%CI 16.9-25.5) than residents (3.2%, 95%CI-0.36-6.7) living in a non-dengue-affected village.

This report documents the first dengue outbreak in Shandong Province, China, in more than 60 years. It underscores the need for medical providers to record patients’ travel histories and to consider dengue in their differential diagnoses.