Differentiating early adult dengue from acute viral respiratory infections – A comparative analysis Tun-Linn Thein,a Eng-Eong Ooi,b,c Jenny GH Lowd & Yee-Sin Leoa# a
Department of Infectious Diseases, Communicable Disease Centre, Tan Tock Seng Hospital, Moulmein Road, Singapore 308433. b c
DSO National Laboratories, 20 Science Park Drive, Singapore 118230. d
Duke-NUS Graduate Medical School, 8 College Road, Singapore 169857. Singapore General Hospital, Outram Road, Singapore 169608.
Abstract The clinical presentations of dengue disease in adults are not fully described. Differentiating dengue from other acute viral respiratory infections (ARIs) is important. We conducted a prospective study from January 2008 to March 2010, recruiting subjects with early febrile illness presenting within the first 72 hours of illness at primary care outpatient clinics. This study evaluates cases enrolled to identify distinguishing clinical features of early dengue infection from ARIs. Acute and convalescent venous blood and nasal swab specimens were collected. Dengue was confirmed by RT-PCR, virus isolation, IgM/IgG seroconversion or fourfold IgG titre increase in paired blood samples. Non-dengue cases were tested for respiratory viruses from nasal swabs by RT-PCR. Dengue was confirmed in 49 patients along with 151 cases of influenza, 10 of parainfluenza and 29 patients of other viruses. The demographics between dengue (n=49) and PCR-positive viral ARI cases (n=190) did not differ significantly except by age (mean 39.1 years vs 33.7 years respectively; P<0.05). Compared with other viral ARIs, dengue patients had significantly more frequent joint pain, vomiting, red eyes, rashes and longer symptoms duration. In the multivariate model, red eyes and leucopenia significantly differentiate between the two groups (P<0.01). This study provides information for early recognition of dengue infection. Keywords: Adult dengue; Acute viral respiratory infections (ARIs).
Introduction Dengue is the most important mosquito-borne viral infection of humans. Worldwide, an estimated 2.5 billion people living in urban areas in tropical and subtropical countries are at risk of dengue infection.[1] Dengue is caused by four closely-related virus serotypes of the #
E-mail: yee_sin_leo@ttsh.com.sg
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genus Flavivirus. Disease spectrum varies from asymptomatic to severe dengue with fatal clinical outcomes, characterized by plasma leakage leading to shock.[2] Dengue re-emerged in Singapore in recent decades despite aggressive vector control. Predominantly a disease of children in the past, it has become an increasingly-recognized problem in adults.[3-5] Early clinical presentations of dengue disease in adults are, however, poorly described. Dengue virus infections are often difficult to distinguish clinically from other acute febrile illnesses, including influenza and other influenza-like illnesses. The ability to suspect and diagnose dengue during its early course of illness is critical for clinicians in order to institute appropriate care and monitoring of the patients.[6] We conducted a prospective study of acute febrile patients comparing dengue and other acute viral respiratory infections (ARIs) to characterize early clinical presentations of dengue in adults and identify early clinical features distinguishing dengue from viral ARIs.
Materials and methods This study prospectively recruited adults aged 18 years and above, who consented to the study, with early undifferentiated fever within 72 hours of onset.[7] All subjects were recruited from four primary health care facilities in Singapore from January 2008 to March 2010. Venous blood and nasal samples were taken at 1–3 days (1st visit) and 4–7 days (2nd visit) after the onset of fever. Convalescent blood sample was collected 3 weeks (3rd visit) later. Demographic, epidemiological and clinical data were collected using structured questionnaires by the research nurses.[7,8] The National Healthcare Group Domain Specific Review Board (DSRB B/05/013) approved the study. Dengue infection was confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR),[9] virus isolation, IgM/IgG sero-conversion or fourfold IgG titre increase in paired blood samples.[8,10] Non-dengue cases were tested for respiratory viruses by direct immunoflorescence assay and RT-PCR from nasal swabs.[11,12] A bench-top Food and Drug Administration (FDA)-approved haematocytometer (iPoch-100, Sysmex, Japan) was used for haematology assessment. Chi-square test and Fisher’s exact tests were used to examine the association between categorical variables and diagnostic values. For continuous variables, two-tailed independent t-test was used. Univariate analysis was performed to determine statistical difference between dengue and acute viral respiratory infections (ARIs), as well as between dengue and other febrile illnesses (OFIs). Multiple logistics regression was also applied to identify the independent predicting factors between dengue and viral ARIs. Receiver operating characteristic analysis was performed to evaluate the predictive model. Data were analysed by using the computer-based SPSS version 16 (SPSS Inc., Chicago, IL, USA). P value less than 0.05 was considered as significant.
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Results A total of 691 patients with acute febrile illness were recruited during the study period. Dengue infection was confirmed in 49 (7.1%) patients, 190 (27.5%) patients were confirmed for acute viral respiratory infections (ARIs) and 452 (65.4%) patients were confirmed for other febrile illnesses (OFIs). ARI cases were further identified to be 151 of influenza, 10 of parainfluenza and 29 of other viruses. Twenty-nine out of 49 dengue cases had dengue EIA or Capture IgG-positive at the first visit or within the first three days of illness, indicating secondary dengue infection. Dengue IgG in acute blood samples also tested positive in 27.4% of ARI cases and 30.5% of OFI cases, reflecting dengue endemicity in Singapore. The demographics between dengue and PCR-positive viral ARI cases did not differ significantly except by age (mean 39.1 years vs 33.7 years respectively; P<0.05). No statistical difference was found between the demographics of dengue and OFIs (Table 1). Sixteen (33%) dengue patients required in-patient care in contrast with 1 (0.53%) of viral ARI and 12 (2.7%) of OFIs. No mortality was recorded in the cohort. Compared with viral ARIs and OFIs, dengue patients had significantly more frequent joint pain, red eyes and longer symptom durations. Vomiting was present in a significantly higher proportion of dengue patients compared to ARI but not OFI cases. Dengue patients had a significantly higher mean aural temperature and more frequent nausea compared to OFIs, but not ARIs. The frequency of abdominal pain, bleeding and nausea was not significantly different between the groups. Significantly lower mean white cell counts and platelet counts were observed in dengue patients than in the other two groups (Table 2). In the multivariate model for dengue and ARIs, having red eyes (relative risk 3.8, P<0.01) and leucopenia (relative risk 5.6, P<0.1) were independent predicting factors for dengue infection. The receiver operating characteristic (ROC) analysis for the model revealed that the area under the (ROC) curve to differentiate dengue from ARI was 0.83 (P<0.001), and had 93.9% sensitivity and 51.0% specificity.
Discussion and conclusion Dengue is the most rapidly spreading mosquito-borne viral disease which constitutes a public health emergency of international concern. In Singapore, together with other countries in the World Health Organization’s Western Pacific Region, dengue has been identified as a major public health issue.[6] In the year 2008 and 2009, 7031 and 4497 dengue cases respectively were notified to Singapore’s health care system, of which 93.7% were older than 15 years of age in both years.[5,13] Because dengue has become predominantly an illness affecting adults, this prospective cohort study was designed to recruit 18-year-old and older patients with undifferentiated fever less than 72-hours duration. All patients were recruited from primary health care facilities in
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Table 1: Demographic characteristics of patients having dengue and acute viral respiratory infections (ARI) in Singapore Dengue (N=49) Mean age + SD Males Ethnicity Chinese Indian Malay Others Singaporeans Travel history Type of housing Condominium Dormitory/Hostel Flat, HDB Landed Worksite Reported past dengue Co-morbidities 2 1 36 7 3 4 6 (4.1) (2.0) (73.5) (14.3) (6.1) (8.2) (12.2) 13 1 144 19 13 6 23 (6.8) (0.5) (75.8) (10.0) (6.8) (3.2) (12.1) 0.094 0.572 33 7 3 6 30 9 (67.3) (14.3) (6.1) (12.2) (61.2) (18.3) 96 35 32 27 125 22 (50.5) (18.4) (16.8) (14.2) (65.7) (11.6) 0.615 0.234 0.689 30 4 364 32 19 23 61 (6.6) (0.9) (80.5) (7.1) (4.2) (5.1) (13.5) 0.323 0.918 39.1 ± 14.8 31 (63.3) ARI (N=190) 33.7 ± 15.1 118 (62.1) P values 0.026 0.510 0.134 259 66 93 34 317 58 (57.3) (14.6) (20.6) (7.5) (70.1) (12.8) 0.197 0.272 0.420 OFI (N=452) 35.1 ± 15.0 291 (64.4) P values 0.077* 0.496 0.078
All P values shown are analysed in comparison to dengue, using Chi-square test and Fisher’s exact test unless otherwise indicated. *Independent t-test was used. Variables shown are numbers with percentage in parentheses unless otherwise stated. SD=standard deviation, HDB=Housing & Development Board.
Singapore between January 2008 and March 2010. Among the 691 patients, 7.1% patients were confirmed to have dengue infection by dengue PCR or IgM sero-conversion in paired blood samples, while acute viral respiratory infections (ARIs) and other febrile illnesses (OFIs) were diagnosed in 27.5% and 65.4% patients respectively. Among the dengue cases reported to the Ministry of Health during 2008 and 2009, on an average, there were 61.3% males, 51.2% Chinese, 64.8% local Singaporeans and 58.9% Housing & Development Board (HDB) flat residents.[5,13] Comparable demographic characteristics among the confirmed dengue cases in our study showed representation of national distributions. In our study, the prevalence of co-morbidities was similar between dengue, ARI and OFI cases. Co-morbidities included
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Table 2: Clinical and laboratory features of dengue and acute viral respiratory infections in Singapore Dengue (N=49) Temperature (°C) ± SD SBP (mmHg) ± SD Pulse rate per minute ± SD Drowsiness Headache Muscle pain Joint pain Loss of appetite Abdominal pain Diarrhea Nausea Vomiting Red eye Rashes Retro orbital pain Swollen lymph node Taste alteration Skin sensitivity Bleeding Haematocrit (%)± SD Haemoglobin (g/dL) ± SD WBC (103/mL ) ± SD Platelet (103/mL ) ± SD Symptom duration days ± SD 38.4 ± 0.8 117.3 ± 18.1 91.2 ± 14.2 24 38 33 29 36 12 6 24 8 18 6 8 1 37 11 1 (49.0) (77.6) (67.3) (59.2) (73.5) (24.5) (12.2) (49.0) (16.3) (36.7) (12.2) (16.3) (2.0) (75.5) (22.4) (2.0) ARI (N=190) 38.2 ± 2.3 122.0 ± 14.6 95.0 ± 14.8 112 151 130 73 129 36 13 63 11 31 0 41 12 126 31 5 (58.9) (79.5) (68.4) (38.4) (67.9) (18.9) (6.8) (33.2) (5.8) (16.3) (0) (21.6) (6.3) (66.3) (16.3) (2.6) P values 0.69 0.06 0.10 0.314 0.823 0.506 0.007 0.684 0.249 0.169 0.112 0.022 0.002 <0.001 0.623 0.329 0.400 0.210 0.643 0.99 0.62 <0.001 <0.001 0.02 OFI (N=452) 38.1 ± 0.8 119.5 ± 16.4 90.2 ± 14.5 259 315 297 168 300 95 39 133 47 66 18 60 30 274 70 11 (57.3) (69.7) (65.7) (37.2) (66.4) (21.0) (8.6) (29.4) (10.4) (14.6) (4.0) (13.3) (6.6) (60.6) (15.5) (2.4) P values 0.005* 0.384* 0.666* 0.462 0.503 0.477 0.002 0.563 0.772 0.269 0.019 0.410 <0.001 0.033 0.797 0.374 0.119 0.413 0.669 0.947* 0.711* <0.001* <0.001* <0.001*
46.2 ± 9.4 15.3 ± 3.3 4.4 ± 2.2 159.2 ± 76.1 9.2 ± 3.9
46.1 ± 8.8 15.1 ± 2.8 7.0 ± 2.8 216.6 ± 77.7 7.4 ± 5.0
46.1 ± 8.6 15.2 ± 2.8 8.6 ± 4.3 240.7 ± 115.7 6.0 ± 4.3
All P values shown are analysed in comparison to dengue, using Chi-square test and Fisher’s exact test unless otherwise indicated. *Independent t-test was used. Variables shown are numbers with percentage in parentheses unless otherwise stated. ARI=acute viral respiratory infections, OFI=other febrile illnesses. SD=standard deviation, SBP=systolic blood pressure, WBC=white blood cell count.
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diabetes, ischaemic heart disease, malignancy and steroid-treated diseases. Some patients had more than one pre-existing co-morbidities. Compared to viral ARI patients, dengue patients were older. In this cohort, having red eyes was an independent predicting factor for dengue infection. In India, a study revealed that 37.3% of adult dengue inpatients were reported to have subconjunctival haemorrhage,[14] while a paediatric study from Viet Nam reported that headache was the most common presenting symptom, followed by conjunctivitis, petechial rash, muscle and joint pain, nausea and abdominal pain.[15] Frequencies of abdominal pain among dengue and viral ARI patients were not different in our cohort. A study from Thailand reported that positive tourniquet test and presence of leucopenia can predict dengue diagnosis.[16] Although tourniquet test is commonly performed to differentiate dengue haemorrhagic disease from OFI, the test is not performed in Singapore.[17] Tanner et al. reported a decision algorithm for the diagnosis of dengue using a combination of platelet count, total white cell count, body temperature, absolute lymphocyte and neutrophil counts.[18] Using fever and leucopenia to predict the diagnosis of dengue was discussed in a larger cohort of older adults presenting with febrile illness in Singapore.[8] Our study further supports leucopenia (WBC <4.5x103/mL) as a useful laboratory feature for differentiating dengue from viral ARIs. Dengue is a disease with a wide spectrum of clinical presentations and often with unpredictable clinical evolution and outcome. It is often difficult to distinguish dengue clinically from other viral ARIs. While other diseases such as chikungunya may mimic dengue infection,[6] none of our subjects in this cohort tested positive for chikungunya virus using inhouse PCR[19] on acute febrile samples. In resource-limited areas where laboratory diagnostic tests are costly or are not available, and access to rapid tests is not consistent, our study supported the use of clinical sign (red eye) and peripheral white cell count to differentiate patients with dengue from acute viral respiratory illness during the early stage. A case report highlighted co-infection of dengue and influenza presenting with undifferentiated febrile illness.[20] Our study did not assess co-infection as only those tested negative for dengue were analysed for respiratory pathogens. However, this phenomenon can be further explored. From our study, it was found that a significantly higher proportion of dengue patients than viral ARIs patients required inpatient care. Dengue patients remained symptomatic for a longer duration than those with viral ARIs. This has implication for the loss of productive days among adults. We hope information from our study may help identify dengue early for appropriate management.
Acknowledgements This study was supported by the National Medical Research Council of Singapore (NMRC/ TCR/005/2008). The authors thank the doctors of the polyclinics for their referral of patients, and research nurses for their assistance in data and clinical sample collection.
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References [1] Guzman MG, Halstead SB, Artsob H, Buchy P , Farrar J, Gubler DJ, et al. Dengue: a continuing global threat. Nat Rev Microbiol. 2010 Dec; 8(12): S7-S16. [2] Gubler DJ. Dengue and dengue hemorrhagic fever. Clin Microbiol Rev. 1998 Jul;11(3): 480-96. [3] Ooi EE, Goh KT, Gubler DJ. Dengue prevention and 35 years of vector control in Singapore. Emerg Infect Dis. 2006 Jun; 12(6): 887-93. [4] Ler TS, Ang LW, Yap GSL, Ng LC, Tai JC, James L, et al. Epidemiological characteristics of the 2005 and 2007 dengue epidemics in Singapore -similarities and distinctions. Western Pacific Surveillance and Response Journal. 2011; 2(2): doi: 10.5365/wpsar.2010.1.1.011. [5] Communicable disease surveillance in Singapore 2009. Singapore: Ministry of Health, 2010. [6] World Health Organization. Dengue: guidelines for diagnosis, treatment, prevention and control. Geneva: World Health Organization, 2009. [7] Low JG, Ooi EE, Tolfvenstam T, Leo YS, Hibberd ML, Ng LC, et al. Early Dengue infection and outcome study (EDEN) - study design and preliminary findings. Ann Acad Med Singapore. 2006 Nov; 35(11): 783-9. [8] Low JG, Ong A, Tan LK, Chaterji S, Chow A, Lim WY, et al. The early clinical features of dengue in adults: challenges for early clinical diagnosis. PLoS Negl Trop Dis. 2011; 5(5): e1191. [9] Lai YL, Chung YK, Tan HC, Yap HF, Yap G, Ooi EE, et al. Cost-effective real-time reverse transcriptase PCR (RT-PCR) to screen for Dengue virus followed by rapid single-tube multiplex RT-PCR for serotyping of the virus. J Clin Microbiol. 2007 Mar; 45(3): 935-41. [10] Chaterji S, Allen JC, Chow A, Leo YS, Ooi EE. Evaluation of the NS1 Rapid Test and the WHO Dengue Classification Schemes for Use as Bedside Diagnosis of Acute Dengue Fever in Adults. Am J Trop Med Hyg. 2011 Feb; 84(2): 224-8. [11] Watzinger F, Suda M, Preuner S, Baumgartinger R, Ebner K, Baskova L, et al. Real-time quantitative PCR assays for detection and monitoring of pathogenic human viruses in immunosuppressed pediatric patients. J Clin Microbiol. 2004 Nov; 42(11): 5189-98. [12] Templeton KE, Scheltinga SA, Beersma MF, Kroes AC, Claas EC. Rapid and sensitive method using multiplex real-time PCR for diagnosis of infections by influenza a and influenza B viruses, respiratory syncytial virus, and parainfluenza viruses 1, 2, 3, and 4. J Clin Microbio. 2004 Apr; 42(4): 1564-9. [13] Communicable Disease Surveillance in Singapore 2008. Singapore: Ministry of Health, 2009. [14] Kapoor HK, Bhai S, John M, Xavier J. Ocular manifestations of dengue fever in an East Indian epidemic. Can J Ophthalmol. 2006 Dec; 41(6): 741-6. [15] Buchy P , Vo VL, Bui KT, Trinh TX, Glaziou P , Le TT, et al. Secondary dengue virus type 4 infections in Vietnam. Southeast Asian J Trop Med Public Health. 2005 Jan; 36(1): 178-85. [16] Kalayanarooj S, Nimmannitya S, Suntayakorn S, Vaughn DW, Nisalak A, Green S, et al. Can Doctors Make an Accurate Diagnosis of Dengue Infections at an Early Stage? Dengue Bull. 1999; 23: 1-7.
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[17] Leo YS, Thein TL, Fisher DA, Low JGH, Oh HM, Narayanan RL, et al. Confirmed adult dengue deaths in Singapore: 5-year multi-center retrospective study. BMC Infect Dis. 2011 May 12; 11(1): 123. [18] Tanner L, Schreiber M, Low JG, Ong A, Tolfvenstam T, Lai YL, et al. Decision tree algorithms predict the diagnosis and outcome of dengue fever in the early phase of illness. PLoS Negl Trop Dis. 2008; 2(3): e196. [19] Ng LC, Tan LK, Tan CH, Tan SS, Hapuarachchi HC, Pok KY, et al. Entomologic and virologic investigation of Chikungunya, Singapore. Emerg Infect Dis. 2009 Aug; 15(8): 1243-9. [20] Lopez Rodriguez E, Tomashek KM, Gregory CJ, Munoz J, Hunsperger E, Lorenzi OD, et al. Co-infection with dengue virus and pandemic (H1N1) 2009 virus. Emerg Infect Dis. 2010 May; 16(5): 882-4.
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