Chronic sequelae complicate convalescence from both dengue and acute viral respiratory illness

Long Covid has raised awareness of the potentially disabling chronic sequelae that afflicts patients after acute viral infection. Similar syndromes of post-infectious sequelae have also been observed after other viral infections such as dengue, but their true prevalence and functional impact remain poorly defined. We prospectively enrolled 209 patients with acute dengue (n = 48; one with severe dengue) and other acute viral respiratory infections (ARI) (n = 161), and followed them up for chronic sequelae up to one year post-enrolment, prior to the onset of the Covid-19 pandemic. Baseline demographics and co-morbidities were balanced between both groups except for gender, with more males in the dengue cohort (63% vs 29%, p<0.001). Except for the first visit, data on symptoms were collected remotely using a purpose-built mobile phone application. Mental health outcomes were evaluated using the validated SF-12v2 Health Survey. Almost all patients (95.8% of dengue and 94.4% of ARI patients) experienced at least one symptom of fatigue, somnolence, headache, concentration impairment or memory impairment within the first week of enrolment. Amongst patients with at least 3-months of follow-up, 18.0% in the dengue cohort and 14.6% in the ARI cohort experienced persistent symptoms. The median month-3 SF-12v2 Mental Component Summary Score was lower in patients who remained symptomatic at 3 months and beyond, compared to those whose symptoms fully resolved (47.7 vs. 56.0, p<0.001), indicating that patients who self-reported persistence of symptoms also experienced functionally worse mental health. No statistically significant difference in age, gender distribution or hospitalisation status was observed between those with and without chronic sequelae. Our findings reveal an under-appreciated burden of post-infection chronic sequelae in dengue and ARI patients. They call for studies to define the pathophysiology of this condition, and determine the efficacy of both vaccines as well as antiviral drugs in preventing such sequelae.


Unfunded studies
Enter: The author(s) received no specific funding for this work.
Long Covid has raised awareness of the potentially disabling chronic sequelae that afflicts 20 patients after acute viral infection. Similar syndromes of post-infectious sequelae have also 21 been observed after other viral infections such as dengue, but their true prevalence and 22 functional impact remain poorly defined. We prospectively enrolled 209 patients with acute 23 dengue (n=48; one with severe dengue) and other acute viral respiratory infections (ARI) 24 (n=161), and followed them up for chronic sequelae up to one year post-enrolment, prior to the 25 onset of the Covid-19 pandemic. Baseline demographics and co-morbidities were balanced 26 between both groups except for gender, with more males in the dengue cohort (63% vs 29%, 27 p<0.001). Except for the first visit, data on symptoms were collected remotely using a purpose-28 built mobile phone application. Mental health outcomes were evaluated using the validated SF-29 12v2 Health Survey. Almost all patients (95.8% of dengue and 94.4% of ARI patients) 30 experienced at least one symptom of fatigue, somnolence, headache, concentration impairment 31 or memory impairment within the first week of enrolment. Amongst patients with at least 3-32 months of follow-up, 18.0% in the dengue cohort and 14.6% in the ARI cohort experienced 33 persistent symptoms. The median month-3 SF-12v2 Mental Component Score was lower in 34 patients who remained symptomatic at 3 months and beyond, compared to those whose 35 symptoms fully resolved, indicating that patients who self-reported persistence of symptoms 36 also experienced functionally worse mental health. No statistically significant difference in age, 37 gender distribution or hospitalisation status was observed between those with and without 38 Covid. Long Covid afflicts a significant proportion of patients after convalescence from Severe 47 Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, and includes symptoms 48 such as fatigue, "brain fog" and even depression, which persist for 3 months or more acute 49 infection (1-3). Yet, this syndrome of post-infectious chronic sequelae is not confined 50 exclusively to SARS-CoV-2, but has also been observed after convalescence from other acute 51 viral infections, one of which is dengue (4). 52 Dengue is an acute mosquito-borne viral illness that afflicts an estimated one hundred 53 million people annually (5, 6). There is no licensed anti-dengue therapeutic, and the only 54 currently licensed dengue vaccine has safety and efficacy concerns (7). The acute symptoms 55 of infection usually last 7-10 days, and range from self-limiting undifferentiated fever, to more 56 severe and potentially fatal dengue haemorrhagic fever and shock (5). Much less however, is 57 understood about post-dengue chronic sequelae. Although symptoms such as fatigue and 58 cognitive impairment have been described post-infection, many of these observations were 59 made retrospectively and thus subject to recall bias, or were derived after a relatively short 60 period of study follow-up (8-12). As such, the true prevalence and duration of post-dengue 61 chronic sequelae remain poorly defined. Such sequelae would not only have a direct impact on 62 patient convalescence, they would also detrimentally affect the economic productivity of many 63 individuals living in dengue endemic areas. Consequently, the true societal and economic 64 impact of dengue is likely underestimated (13). 65 To understand the true prevalence of post-dengue chronic sequelae, we designed a Mobile-66 phone Application for Information extraction in Dengue (MAIDEN). The use of MAIDEN study visits, thus minimising study costs and avoiding high participant drop-out rates often 69 associated with large prospective studies. In addition, we also took advantage of MAIDEN to 70 explore the impact of chronic sequelae in patients with acute viral respiratory infections (ARI), 71 another highly prevalent group of acute viral infections prior to the emergence of SARS-CoV-72 2, but in which the occurrence of long-term sequelae is even more poorly defined. We 73 prospectively enrolled two separate cohorts of patients with confirmed dengue and ARI and 74 followed them for up to one-year post-illness onset. Our findings suggest that chronic sequelae 75 such as fatigue and central nervous system (CNS)-related symptoms are prevalent in adults 76 after acute dengue, and also affect a sizeable proportion of patients post-ARI. 77

Study Participants 79
Patients were recruited from the inpatient wards, emergency department and staff

Clinical data collection 107
At enrolment after informed consent, relevant demographic and clinical data were 108 collected from patients' medical records. Patients were sent a web link via e-mail to download 109 the MAIDEN application onto their mobile phone, as well as a unique user-ID and password 110 to enable them to access the application. A member of the study team then provided a short 111 tutorial on how to use MAIDEN (Fig 1A). At each visit, patients would enter information 112 regarding symptoms experienced (including the absence or presence of fatigue, somnolence, 113 headache, concentration impairment and/or memory impairment) and self-reported overall 114 health into MAIDEN (see Supporting Information S1 for the full list of questions). The overall 115 health assessments were adapted from the SF-12v2® health survey, which is a validated tool for self-reported physical and mental wellbeing measurement (14-17). Briefly, the SF-12v2® 117 consists of 12 questions that measure eight health domains to assess physical and mental health. Patients were followed-up daily for the first 7 days, weekly from weeks 2 -8, and then 124 monthly from month-3 onwards, up to one-year following acute illness. Except for the first 125 visit at study enrolment, patients were not required to attend the study site in-person, and would 126 be sent reminders by either short messaging system (SMS) or push notification to enter data 127 remotely into MAIDEN when each study "visit" was due. If patients encountered any technical 128 difficulties or had questions about the study, they could contact the study team directly either 129 via phone call or email, or through a direct messaging system within MAIDEN. All data entered 130 into MAIDEN was stored on a secure cloud server and downloaded onto a data management 131 platform for analysis. 132

Definitions 133
We defined "chronic sequelae" as symptoms (fatigue, somnolence, headache, 134 concentration impairment or memory impairment) lasting for at least 3-months post-infection. 135 A patient's symptoms were considered resolved if they did not report any symptoms for at least 136 2-months after the last date of symptoms reported, and were considered lost to follow-up if 137 they did not enter any data into MAIDEN for more than a 2-month period.

Statistical Analysis 139
Differences in demographic features, co-morbidities, prevalence of symptoms at 140 enrolment and MCS between the dengue and ARI cohorts, and those with and without chronic 141 sequelae were analysed using the Fisher's exact test for categorical variables or Mann-Whitney 142 test for continuous variables. Time to resolution of symptoms in both the dengue and ARI 143 cohorts were analysed using Kaplan-Meier analyses. The SF12v2 MCS was calculated using 144 the Optum® PRO CoRE software. P-values <0.05 were considered statistically significant. All 145 statistical analyses were performed using GraphPad Prism version 9.2.0. 146

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A total of 209 patients were enrolled during the study period, with 48 patients in the 148 dengue cohort, and 161 patients in the ARI cohort. 81.3% (39/48) of dengue patients and 98.1% 149 (158/161) of ARI patients completed at least 3 months of study follow-up (Fig 1B). Table 1  150 shows the demographic and clinical profile of both patient cohorts. Baseline demographics 151 such as age, ethnicity and co-morbidities were balanced between both groups, except for 152 gender, with more males in the dengue cohort (63% vs. 29%, p<0.001). More patients in the 153 dengue cohort were hospitalized compared to those in the ARI cohort (77.1 % vs 18.1%, 154 p<0.001), reflecting differences in clinical management between these two disease types. Only 155 one patient had severe dengue, as defined by the World Health Organization (WHO) 2009 156 dengue classification scheme (18). Within the ARI cohort, the specific viral etiology was tested 157 for in 29 patients. Among these patients, influenza virus and rhinovirus were the most common 158 etiologies identified (Table 1). were the most commonly reported symptoms in the dengue cohort, while lethargy and 170 headache were most common in the ARI cohort (Table 1). Amongst patients with at least 3-171 months of follow-up, 18.0% in the dengue cohort and 14.6% in the ARI cohort experienced 172 chronic sequelae (Table 2). In the dengue cohort, fatigue, concentration impairment and 173 memory impairment were the most commonly reported chronic symptoms, while fatigue and 174 headache were most prevalent in the ARI cohort. Kaplan-Meier analysis indicated that fatigue 175 and CNS-related symptoms resolved within weeks of convalescence in the majority of dengue 176 patients. However, the rate of full recovery then plateaued and even persisted in some patients 177 until the end of our observation period (Fig 2A). Similar trends were observed in patients with 178 ARI (Fig 2B). No statistically significant difference in age, gender distribution or 179 hospitalisation status was observed between those with and without chronic sequelae (Table 3). 180  Table 3. Demographics of patients with and without chronic sequelae. Chronic sequelae is 185 defined as persistence of symptoms (any one of fatigue, somnolence, headache, concentration 186 impairment or memory impairment) for at least 3 months.

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In both cohorts, the median month-3 MCS was lower in patients who remained 189 symptomatic at 3 months and beyond, compared to those whose symptoms fully resolved (Fig  190   3), indicating that patients who self-reported persistence of symptoms beyond 3 months also 191 experienced functionally worse mental health.  dengue. This is even less so for acute respiratory viral infections such as influenza and 206 adenovirus. In one study of dengue patients, an association was found between the FcγRIIa 207 (FcγRIIa-131HH) gene polymorphism, the presence of autoimmune markers and symptom 208 persistence (9). Apart from this report, no other studies to date explored the causes of post-209 dengue chronic sequelae. We used MAIDEN as a study tool for remote data-collection in order to overcome the high 225 financial costs and participant drop-out rates often associated with large prospective studies. 226 We reasoned that remote data collection would promote better compliance from study 227 participants in view of the convenience afforded through remote data collection. Indeed, overall 228 study compliance was good with over 90% of patients completing at least 3 months of study 229 follow-up. Besides improving study visit compliance, mobile data collection also allows for immediate pooling of data into a centralized data warehouse, making real-time data analysis 231 possible. Given these benefits, and the fact that over 80% of the world's population own a 232 smartphone (23), we envisage that mobile phone applications such as MAIDEN could be a 233 useful adjunct tool not only in the conduct of observational cohort studies, but also in the 234 clinical trial space where such applications could be used for adverse event tracking and 235

reporting. 236
A strength of our study is its prospective design, which avoids the problem of recall bias 237 often associated with retrospective studies. The study follow-up period of one year also enabled 238 the tracking of patients longitudinally over time, allowing for clearer evaluation of time to 239 symptom resolution. Although the symptoms reported by patients were subjective in nature, 240 the use of the validated SF12v2 health outcomes questionnaire allowed for a functional 241 assessment of each study participant's overall mental health. Indeed, we showed that patients 242 who reported persistence of fatigue and/or CNS-related symptoms beyond 3 months had a 243 significantly lower MCS then their counterparts whose symptoms lasted less than 3 months, 244 indicating that self-reported chronic sequelae translates into functionally worse mental health 245

outcomes. 246
A limitation of our study is that patients in the ARI cohort were not tested specifically for 247 DENV, and hence we are unable to completely exclude co-infection. We also acknowledge 248 that the hospitalisation status was imbalanced between the two study cohorts, with a 249 significantly higher proportion of the dengue cohort hospitalised at the time of enrolment, 250 compared to the ARI cohort where the majority of patients were ambulatory. As such, we 251 avoided making head-to head comparisons between the two cohorts. 252 In conclusion, we show that persistent fatigue and CNS-related chronic sequelae, as well 253 as poorer overall mental health, occur in a significant proportion of both dengue and ARI 254 Statistics to compare the median MCS between groups was calculated using the Mann-Whitney 287 test. *** = p < 0.001, ****= p <0.0001, ns = not significant.