Control of COVID-19 in China likely reduced the burden of multiple other infectious diseases

Dear editor, We read with great interest the recent issue 1 , 2 regarding the activity of influenza during COVID-19 pandemic, which demonstrated the reduction of influenza in Brazil and Singapore at the same time. The similar findings were also reported in Japan and Taiwan, in which the activity of seasonal influenza was lower in 2020 than before. 3 , 4 The decreased activity of seasonal influenza could be due to the implementation of many infection control measures to prevent the spread of SARS-CoV-2 during COVID-19 pandemic. 3 , 4 Therefore, we hypothesis that these interventions can also positively impact on other respiratory infectious diseases, such as pulmonary tuberculosis (TB), human immunodeficiency virus (HIV) and Hepatitis C virus (HCV) infections. In this study, we compared the weekly confirmed TB, HIV and HCV cases during COVID-19 outbreak in the 2020 season vs 4 previous seasons. In this study, we examined this issue using nationwide surveillance data on infectious diseases from 2017 to 2020 provided by the Centers for Disease Control and Prevention (CDC) in Taiwan. 5 We compared changes across the first 20 calendar weeks of 2020 with the same period of 2017, 2018, and 2019. Theil-Sen trend test was used to calculate the trend of each event and slope difference in comparison between years. 6 During the first 20 weeks of 2020, a total of 2662 confirmed TB cases were reported, which was lower than those of 2019 (n = 3307), 2018 (n = 3512), and 2017 (n = 3563), with a significant slope difference between 2020 and each of prior years (Figure 1 A). In contrast, this kind of declining trend of TB during COVID-19 pandemic was not observed for HIV and HCV cases (Figure 1B and 1C). Figure 1 The trends of infectious events (TB, HIV, and HCV) during the first 20 calendar weeks of 2020 were compared to the events during the corresponding time period in 2017, 2018, and 2019. (A) The COVID-19 outbreak was successfully contained after initiating cotrol measures from the 2nd week, except for some imported cases peaked in the 12th week; the weekly TB cases showing slow decline of TB cases after fitiging COVID-19 outbreak, and significsnt trend difference of TB in 2020 (slope = -2.861) compared to 2019 (slope = 0.899), 2018 (slope = 1.500) and 2017 (slope = 0.674); (B) weekly HIV cases showing no significant trend difference of HIV in 2020 (slope = 0.000) compared to 2019 (slope = -0.600) and 2017 (slope = 0.222), except for 2018 (slope = 0.862); (C) weekly HCV cases showing no significant trend difference of HCV in 2020 (slope = -0.200) compared to 2019 (slope = 0.122), 2018 (slope = 0.125), and 2017 (slope = 0.000). Figure 1 In this study, we had two major findings. First, the prevention measures for containing SARS-CoV-2 transmission may explain the decline of TB trend. Since early 2020, the Taiwan government and the public have widely promoted measures such as wearing surgical masks, respiratory hygiene, handwashing, maintaining social distance, and suspension of large crowd events 7 , 8 and these interventions may also help to contain the spreading of TB. The trend of the decline of TB in this COVID-19 outbreak was more prominent during the 11th-20th calendar weeks than 1st-10th weeks (n= 1201 vs n= 1461). The slope difference between upward trend till the peak (slope = 2.000) and downward trend from the peak (slope = -6.750) reached statistical significance in 2020 (trend difference = 8.750, p = 0.027). The downward speed of decline of TB (from the first case of COVID-19 identified in the second week down to 20th week) was rather slower than that of decreasing influenza activity (from a peak in the second week down to zero case in the 9th week) with a significant trend difference (slope difference = -12.064, p = 0.010). The slower TB decline may probably be due to the longer incubation time of TB activity and some reactivated nature of TB disease, that patients might acquire TB before the COVID-19 outbreak. Second, we observed that the trends of HIV and HCV infections as control groups did not change as that of TB in this study in spite of the aggressive implementation of infection control measures during this period. The difference might be due to the different transmission routes between TB and comparators of HIV and HCV. TB and COVID-19 are transmitted via the respiratory tract, so the infection control measure for SARS-CoV-2 infection can be helpful for TB control, too. In contrast, HIV is mainly transmitted through sexual behaviors and HCV is a blood-borne disease that can be spread through contamination by blood transfusion, needle or syringe use. Therefore, the current measures for containing the SARS-CoV-2 transmission cannot provide additional help for HIV and HCV control. Furthermore, the maintenance of HCV and HIV trends does not support to consider that physicians would less report infectious diseases like TB while devoted to fighting against the COVID-19 outbreak. The limitation of the study is that we could not obtain the number of tests for Mycobacterium tuberculosis (MTB). Thus, there was a possibility of confounding factor that whether the COVID-9 outbreak may have lowered the identification of TB through changes in the behavior of symptomatic individuals seeking medical attention or in physicians’ inclination to test for MTB. In conclusion, we noticed the significant decline of TB activity during fighting against COVID-19 outbreak in Taiwan. Droplet aerosol precaution by prevention measures may offer success in containing SARS-CoV-2 transmission and collateral benefits in TB controls. We also highlight TB diagnosis which should not be forgotten by a physician for patients with respiratory symptoms during the COVID-19 outbreak.

Dear Editor, 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 acute-care 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 From epidemiological-week 1, 2017 through epidemiological-week 52, 2019, the mean weekly influenza positivity rate was 12.9% (standard deviation [SD] 6.7%) (Figure 1 ). In 2017, the year experienced increased influenza activity in January-February (epidemiological-weeks 2-9, 2017), March-April (epidemiological-weeks 11-15, 2017), and May-July (epidemiological-weeks 18-29, 2017, May-Jul). In 2018, influenza activity was highest in the first 10 weeks (epidemiological-weeks 1-10, 2018, January-March) and last 11 weeks (epidemiological-weeks 42-52, 2018, October-December) of the year. The high influenza activity continued into the first 4 weeks of 2019 (epidemiological-weeks 1-4, 2019, January). Figure 1 Weekly Influenza Positivity Rates (%) in TTSH, by epidemiological week, 2017-2020 (primary axis), and Number of new COVID-19 cases nationally and in TTSH in epidemiological-weeks 1-14, 2020 (secondary axis). Figure 1 In 2019-2020, a distinct bimodal increase in influenza activity corresponding to the 2019 southern-hemisphere influenza season (epidemiological-weeks 24-32, 2019, June-July) and 2019/2020 northern-hemisphere influenza season (epidemiological-weeks 48-52, 2019, November-December; epidemiological-weeks 1-5, 2020, January-February) was observed (Figure 1). From epidemiological-weeks 5 to 11, 2020, influenza activity took a dramatic decline by 70.2 percentage points from 17.8% (epidemiological-week 5) to 5.3% (epidemiological-week 6), then halved to 2.7% in epidemiological-weeks 7 and 8 respectively, followed by further decline to 0.8-1.6% (epidemiological-weeks 9-12), to 0% for two consecutive weeks (epidemiological-weeks 13-14). In the last three years, weekly influenza activity has not fallen below 2%. Of note, the weekly respiratory samples tested have increased significantly from a mean of 202.3 (SD 41.8) samples per week (epidemiological-week 1, 2017 through epidemiological-week 52, 2019) to 322.0 (69.2) samples per week (epidemiological-weeks 1-14, 2020) (P<0.0001). There were 228 and 194 samples tested for influenza in epidemiological-weeks 13 and 14 respectively. Our findings corroborated with national data on influenza activity, which reported on a weekly-basis the influenza activity in the preceding four weeks. National influenza activity plunged from a mean of 57.3% in the first 6 weeks of 2020 to 4.6% in epidemiological-week 11 and 3.5% in epidemiological-week 14. 9 The trough national influenza activity in the past three years was 15.6%. During this period, influenza vaccination uptake among TTSH patients has not increased and no large-scale national campaigns to actively promote influenza vaccination has taken place. There was an exponential increase in the number of new COVID-19 cases from three in epidemiological-week 4 to 74 and 387 in epidemiological-weeks 11 and 14 (week ending April 4, 2020) with TTSH having managed 784 (65%) of the cases (Figure 1). Despite increased vigilance for influenza in the management of suspect COVID-19 patients, the detection rate of influenza declined, as the number of COVID-19 cases increased. Whilst influenza activity in temperate Europe and the US have remained high, influenza activity in tropical Singapore took an unprecedented steep decline. This is likely the unintended but pleasant consequence of suspension of mass gatherings, social distancing, and promotion of social responsibility to stay at home when unwell, in response to the COVID-19 pandemic. Declaration of Competing Interest None

Pertussis (whooping cough) epidemics persist globally despite high vaccine coverage among infants and young children. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity, resulting in a pool of unprotected adolescents and adults. However, pertussis is generally less severe in adolescents and adults, and this difference in presentation means it can often be unrecognised by healthcare professionals, meaning that it is largely under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology and mortality in school-aged children, adolescents and adults in Europe. A formal statistical comparison (e.g. using meta-analyses) was not possible because of the mix of methodologies reported. There were 69 epidemiological studies and 19 mortality studies identified for review. Over the past decade, the reported incidence of notified pertussis cases varied widely between European countries, which is likely associated with differences in surveillance systems, diagnostic techniques and reporting regulations. However, several studies show that pertussis is circulating among adolescents and adults in Europe, and although pertussis-related morbidity and mortality are highest in infants, there is evidence that adults aged > 50 years are at increased risk. For example, in a hospital-based surveillance study in Portugal, between 2000 and 2015, 94% of hospitalised pertussis cases were infants aged   65 years). Very few European countries currently include pertussis boosters for adults in the national immunisation strategy. In addition to increasing pertussis vaccination coverage in adolescents and adults, mitigation strategies in European countries should include improved diagnosis and treatment in these populations. Supplementary Information The online version contains supplementary material available at 10.1007/s40121-021-00520-9.