Lam et al. reported that tropical countries showed fluctuating incidence of influenza throughout the year. 1 The emergence of COVID-19 in China during the northern hemisphere winter season of 2019/2020 resulted in worldwide transmission. 2 Influenza activity has remained elevated in many northern-hemisphere temperate countries, as COVID-19 swept across the globe. As of mid-March 2020, influenza circulation remained high in Europe 3 and the United States (US) although there was some decline in activity. 4 In early-April, influenza activity was still elevated in the US. 5 COVID-19 was first imported into Singapore on January 22, 2020 by a tourist from Wuhan. The tropical city-state's strategy was that of containment. 6 On February 7, 2020, towards the end of epidemiological-week 6, Singapore implemented measures under the Disease Outbreak Response Condition (DORSCON) Orange. 7 During DORSCON Orange, non-essential large-scale events were cancelled or deferred, and daily temperature and health checks were performed in schools and at workplaces. Individuals who were unwell were encouraged to rest at home and to wear a face mask if they absolutely had to go out (such as to medically attend at doctor's offices), and to avoid coming into close proximity and sustained contact with others.We report the unintended but pleasant consequences of public health measures implemented to contain COVID-19 on influenza activity in tropical Singapore.We evaluated the weekly influenza positivity rates from epidemiological-week 1, 2017 (week ending January 7, 2017) through epidemiological-week 14, 2020 (week ending April 4, 2020), at Tan Tock Seng Hospital (TTSH), a 1600-bed adult acutecare general hospital co-located with the 330-bed National Centre for Infectious Diseases that is the designated national referral centre for the management of COVID-19. The Centre manages the majority of COVID-19 patients in Singapore. Patients admitted for respiratory illness and suspected of influenza infection had clinical respiratory specimens tested for influenza A and B via polymerase chain reaction test. Routine influenza surveillance on all patients hospitalised at TTSH has been performed since the 2009 influenza pandemic. 8
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Fig. 1. Staff acute respiratory infection (ARI) clusters (primary axis) and staff absenteeism from ARI (secondary axis) Tan Tock Seng Hospital (TTSH) and National Centre for Infectious Diseases (NCID) (epidemiological week 1 in 2019 to epidemiological week 27 in 2020).
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