Clinical Characteristics of Dengue Shock Syndrome in Vietnamese Children: A 10-Year Prospective Study in a Single Hospital

We present the clinical features, management, and outcomes for 1719 Vietnamese children with dengue shock syndrome enrolled in a 10-year prospective study in a single center, to provide the first comprehensive description of this increasingly important disorder.

Infection with any serotype can cause a broad range of disease manifestations, from inapparent infection to severe and fatal disease [4]. The most notable complication is an unexplained vasculopathy that manifests as a transient increase in vascular permeability resulting in leakage of plasma from the circulation. Substantial plasma losses may occur, leading to the potentially fatal dengue shock syndrome (DSS). Although adults do experience shock, vascular leakage is generally more severe in young children [5], and in endemic areas DSS is seen primarily in the pediatric population. Thrombocytopenia and coagulation derangements also occur, and a variety of bleeding manifestations ranging from minor skin petechiae to major mucosal bleeding may be seen. Neither vaccines nor specific therapies are currently available; careful clinical observation and judicious use of intravenous fluid therapy, in particular urgent shock resuscitation for DSS, are the foundations for successful management [6]. Many individuals with DSS respond to resuscitation with crystalloid solutions, but patients with profound or protracted shock often require additional support with colloid solutions and are at risk of developing respiratory compromise due to ongoing plasma leakage. Mortality rates for DSS vary from <1% to >10% depending on the severity of the cases reported, the level of monitoring available, and the experience of the attending healthcare personnel [7][8][9].
Despite the increasing burden of dengue globally, only a few small retrospective reports have described the clinical characteristics, management, or outcomes of DSS [8,10,11]. At the Hospital for Tropical Diseases (HTD) in Ho Chi Minh City, a prospective observational study aiming to enroll all children presenting with DSS was conducted from 1999 to 2009. Here we present data on >1700 cases collected during this 10-year period, providing the first comprehensive description of the clinical features of DSS in children.

Study Design and Participants
At HTD, children aged <15 years with DSS are managed on the pediatric intensive care unit (PICU). In 1999, we commenced a prospective observational study in which children admitted with clinically diagnosed DSS-that is, a history consistent with dengue, with hemodynamic compromise (either narrowing of the pulse pressure or hypotension for age, with evidence of impaired perfusion) thought by the treating clinician to be due to vascular leakage and to require volume resuscitation-were eligible to participate. Patients transferred from other facilities for tertiary care after initial resuscitation were not eligible. A double-blind randomized controlled trial (RCT) that was conducted within the study period (1999)(2000)(2001)(2002)(2003)(2004) comparing different fluid solutions for initial resuscitation has been reported previously [7]. Both studies were approved by the HTD ethical committee and the Oxford Tropical Research Ethics Committee.

Study Procedures and Data Collection
Following written informed consent by a parent or guardian, trained study physicians enrolled participants immediately after diagnosis of shock. Demographic characteristics, clinical history, and examination findings were recorded on a structured case report form at enrollment and then daily until discharge or death, together with detailed information about all therapeutic interventions and supportive care required. Specimens for dengue diagnostics were obtained at enrollment and discharge. All survivors were asked to return for follow-up assessment 1 month later.
A core group of senior clinicians supervised patient care throughout the study period, following the management guidelines for pediatric DSS at HTD. The routine initial regimen consisted of 25 mL/kg Ringer's lactate solution over 2 hours, with colloid solutions (dextran or starch) reserved for children presenting with profound shock. However, during the RCT, patients were randomized to receive 1 of these 3 fluid solutions, at the same rate but blinded, for their initial resuscitation [7]. A standardized schedule of Ringer's lactate was then used for all patients, involving staged reductions at specific time intervals, aiming for maintenance fluid therapy after 8 hours. Patients who failed to stabilize within 2 hours, or who deteriorated during the mandatory 36-to 48-hour period of close observation, received 10-15 mL/kg infusions of rescue colloid plus inotropes, blood products, or other therapy at the discretion of the treating clinician.
Cardiovascular status was monitored at least hourly until stable for 24 hours, and subsequently every 4 hours. The capillary hematocrit was measured at baseline, approximately 2 and 6 hours after study entry, and then every 12 hours or in the event of cardiovascular deterioration. A complete blood count was performed once daily, whereas other laboratory tests (eg, liver/renal function) were checked on clinical grounds rather than according to a defined study schedule. Disease classification was performed using the World Health Organization (WHO) 1997 and 2009 criteria (Supplementary Appendix 1) [4,12].

Dengue Diagnostics
Dengue immunoglobulin M and immunoglobulin G (IgG) capture enzyme-linked immunosorbent assays were performed on paired enrollment and early convalescent specimens, together with reverse transcription polymerase chain reaction (RT-PCR) on the enrollment specimen [13][14][15]. Seroconversion and/or detection of DENV RNA in plasma defined laboratory-confirmed cases (Supplementary Appendix 2). A positive dengue-specific IgG on or before day 7 of illness defined a secondary infection, whereas 2 negative dengue-specific IgG results, at least 1 obtained after day 7, were required to define a primary infection.

Statistical Analysis
Continuous and categorical variables were summarized as median and interquartile range (IQR), or frequency and percentage, respectively. All analyses were performed with the statistical software R, version 2.15.0 [16].

RESULTS
From 1999 to 2009, a total of 1810 of 1847 children (98%) admitted to PICU with clinical DSS participated in the study. In 19 cases, both RT-PCR and paired serology were negative, whereas in 72 cases the results were inconclusive; in the remaining 1719 cases (95%) dengue was confirmed, with the infecting serotype identified in 1209 of 1647 cases (73%) for which RT-PCR was performed. Among the confirmed dengue patients, 503 (29%) participated in the RCT, with the remainder enrolled in the observational study. Almost all cases came from the local catchment area, with <5% of cases transferred from elsewhere; however, 2 patients were enrolled in error, having already received parenteral fluids for shock resuscitation prior to transfer.

Characteristics at Presentation With Shock
Demographic information and selected clinical characteristics for all 1719 patients with confirmed dengue are described in Table 1. For most parameters, data were missing in <5% of cases. The median age was 10 years, varying by year of study from age 9 to 11 years. The median day of illness at shock was consistently 5 (IQR, 4-6) for each study year, although 62 patients (4%) overall presented on illness day 3.

Progress in Hospital
Because many patients in the RCT were randomized to a colloid for initial resuscitation, information on management and complications after enrollment is presented for the observational study and RCT groups separately ( Table 2). Apart from the greater colloid usage, there was little difference between the 2 study groups other than a slightly higher proportion of minor skin bleeding observed in the RCT group. Considering gastrointestinal bleeding occurred most frequently (n = 61), compared to epistaxis (n = 36), gum bleeding (n = 22), or unusual vaginal bleeding (n = 21). The bleeding was clinically severe in 31 cases, 26 requiring transfusion (18 during active resuscitation, and 8 during the recovery phase), 4 resulting in compensated anemia at discharge, and 1 case involving a critical organ (spinal cord hemorrhage, confirmed by magnetic resonance imaging). Although most severe bleeding primarily involved the gastrointestinal tract (n = 15), 7 children had isolated severe skin bleeding, mainly at sites of invasive procedures, and 4 of 7 required transfusion. Platelet concentrates were not available during the study, but children with severe coagulopathy and active bleeding received fresh frozen plasma or other blood products at the discretion of the treating clinician.
The evolution of hematocrit and platelet values is shown in Figure 1. The median maximum hematocrit was 50% (IQR, 47%-52%), documented at presentation in most cases (1484/ 1719 [86%]). Among patients with both enrollment and 1month follow-up values, 755 of 832 (91%) had at least 20% hemoconcentration at enrollment. The hematocrit declined rapidly during the first 4 hours of resuscitation, later rising again in the majority of children. In contrast, the platelet nadir (median, 28 000 cells/µL [IQR, 19 000-40 000 cells/µL]) occurred most frequently 1 day after onset of shock (720/1718 [42%]). Although a transient drop in platelet count was seen in all cases, in 25 of 1718 cases the nadir remained >100 000 cells/µL. Coagulation profiles were performed infrequently and are not reported here, but the abnormalities observed were consistent with previous reports [17,18]. Liver enzyme levels were checked in approximately 60% and were moderately elevated at shock, with aspartate aminotransferase levels consistently higher than alanine aminotransferase levels.
All patients would have fulfilled the 2009 WHO criteria for severe dengue, whereas only 939 of 1642 (57%) of the children with sufficient data to allow classification at enrollment would have been categorized as having dengue hemorrhagic fever (DHF). Using all available information from the acute illness and any follow-up visits, 1202 of 1705 (70%) of the patients eventually fulfilled the 4 criteria for DHF, with the remainder classified as having dengue fever by default.

Outcome
During the 10-year study, only 8 patients died (1 infant and 7 children; Table 3), although 2 additional DSS-associated deaths outside the study were identified from hospital records. In 3 of 8 cases, shock occurred early, on illness day 4. All 8 patients developed profound shock within the first 12 hours, requiring multiple colloid infusions plus inotropic support and with rapid development of significant fluid overload. The interval from admission to death was generally short (median, 34 hours [range, 11-87 hours]), although 1 child with multiorgan failure was taken home moribund after 4 days. Major bleeding requiring transfusion was apparent in 7 of 8 cases before death. Overt organ dysfunction was very uncommon. Other than in association with prolonged shock (Table 3, cases 7 and 8) no patient in the cohort had clinically significant hepatic, renal, or neurological compromise, except for the child with spinal cord hemorrhage and 1 other child with profound shock, liver failure, and coma. These 2 children both eventually made a full recovery with supportive care.

Dengue Serotypes and Immune Status
The relative abundance of dengue serotypes identified in the patient cohort over time is presented in Figure 2A. With increasingly sensitive diagnostics, successful serotype identification increased, from 30%-50% initially to >80% after 2007. In 1999, DENV-3 was the most common serotype seen, replaced by DENV-4 peaking in 2001, DENV-2 peaking in 2004, and finally by DENV-1 extending from 2005 to 2009. Almost all patients had an IgG response consistent with secondary infection, although 106 of 1719 (6%) of cases were unclassifiable. The pattern of serotypes observed was very similar to that seen among 1509 children with secondary dengue without shock enrolled into a separate observational study between 2001 and 2009 ( Figure 2B; unpublished data).
Only 6 cases had clear primary infections, including 4 infants aged <18 months, and 2 children aged 7 and 12 years (Table 4). Immune status was suggestive of primary disease in 4 of the 5 other children aged <18 months (no information in 1 case), whereas all 157 children aged 18-60 months with classifiable immune status had secondary dengue. Infants may be underrepresented in the cohort, however, as many parents elect to take young children to 1 of 2 specialist pediatric hospitals nearby. All of the patients with definite primary cases Figure 1. Box plots describing changes in hematocrit (A) and platelet count (B) during the evolution of the illness. Hematocrit data are presented for the 24 hours following admission, whereas platelet data are presented daily for the first 4 days, together with the discharge day and follow-up values for both parameters. The numbers displayed below each box plot represent the number of patients included within that time interval. If multiple values were recorded during any time interval, we chose the highest hematocrit and the lowest platelet count, respectively, for that patient. The hematocrit graph excludes data from the 73 patients with dengue shock syndrome with mucosal bleeding at presentation. recovered, although 2 infants required colloid infusions. However, one 11-month-old boy with indeterminate/possible primary dengue died with profound shock.

DISCUSSION
Here we present the first comprehensive description of the clinical features of DSS in children, using data gathered prospectively over 10 years on 1719 patients managed in a single Vietnamese institution. More than 95% of all children admitted with DSS during the study period were evaluated. Because prior shock resuscitation might confound the clinical picture, we focused on direct admissions only. A few cases were missed, including 2 children who died, but overall the results are representative of the clinical spectrum of patients with DSS admitted directly to a busy hospital in a hyperendemic region.
Apart from infants aged <18 months, virtually all children had secondary dengue, in line with established concepts of pathogenesis [19,20]. We observed DSS caused by all 4 dengue serotypes during the 10-year study; the pattern of serotype replacement over time was similar to that seen among children with secondary infections enrolled in a contemporaneous study of hospitalized dengue without severe manifestations, and also to the relative virus prevalence identified by passive surveillance in southern Vietnam during the same time period [21]. Thus, the viruses associated with DSS appear to be representative of the virus population affecting the wider community, with no evidence that a particular serotype contributes to a greater risk for shock. Notably, however, 3 of 8 deaths were associated with DENV-3, although the total number of DENV-3 infections identified was small. Because a number of interacting host and viral factors influence an individual's propensity to develop severe vascular leakage [19], only very detailed studies can establish whether particular viral characteristics do confer an increased risk for DSS or death.
The clinical signs and symptoms documented were generally consistent with empirical descriptions of DSS [4]. However, 9% of all patients were still febrile at presentation. Increased permeability commences during the febrile phase, but shock develops only when leakage exceeds the capacity of the homeostatic compensatory mechanisms to maintain adequate plasma volume [22,23], potentially compounded by functional cardiac impairment [24]. Although defervescence and shock are often temporally linked, it is important that clinicians managing suspected dengue cases understand that DSS can occur earlier. Identification of more reliable warning signs of likely deterioration would be useful both for individual case management and to facilitate effective use of limited healthcare resources.
In agreement with other studies [7,25], a considerable number of DSS patients had no bleeding during the illness. Severe bleeding was uncommon and primarily from the gastrointestinal tract, although massive soft tissue bleeding necessitating transfusion occurred in 4 children. Again consistent with other studies [25,26], almost one-third of cases did not achieve the WHO 1997 classification for DHF, mainly due to failure to fulfill the hemorrhage and/or plasma leakage criteria as thrombocytopenia was almost universal. If positive, a tourniquet test might have allowed classification as DHF rather than dengue fever in 357 additional cases, but several studies have demonstrated poor utility of the test in clinical practice, and it is infrequently performed in Vietnam [25,27]. We did not perform radiological investigations to identify plasma leakage unless clinically indicated, reflecting real-world practice. Thus, diagnosis of leakage typically rested upon demonstration of hemoconcentration, yet hemoconcentration below the WHO threshold of 20% has been noted previously in DSS patients [11]. Because patients must be treated according to their actual clinical status, it is apparent that the 1997 WHO classification system is not suitable for individual case management in real time.
The case fatality rate was extremely low (0.5%). Most patients recovered well with the standard crystalloid regimen or following a single colloid bolus, and requirement for additional colloid therapy, inotropic support, and/or blood products was infrequent. Prompt diagnosis and immediate admission to PICU with management coordinated by a highly experienced team undoubtedly contributed to this favorable outcome. In line with WHO principles [4], the unit operates a generally conservative fluid management policy after initial resuscitation, relying on frequent clinical assessments and regular wardbased hematocrit measurements to limit fluid administration to the minimum required, reducing the risk of fluid overload.  However, our study focused on direct admissions, and it is clear that external referrals with prolonged shock or established fluid overload are more difficult to manage and have correspondingly higher mortality rates [8]. Only a very small number of patients with confirmed primary dengue were included in the cohort, and all recovered quickly without notable complications. However, 1 death occurred in a suspected primary case, underlining the view that primary dengue can result in severe and even fatal disease [28][29][30]. Given that immune status could not be defined in 6% of patients, some primary cases might have been missed, but the number is likely to be small. In summary, we present a comprehensive clinical description of DSS in a large cohort of Vietnamese children. We demonstrate that with prompt intervention and assiduous clinical care by experienced staff, the outcome of this potentially fatal condition can be excellent. As the emerging dengue pandemic spreads to new geographical locations, it is important that this accumulated experience be translated into practical advice for clinicians newly exposed to this severe complication of a common disorder.

Supplementary Data
Supplementary materials are available at Clinical Infectious Diseases online (http://cid.oxfordjournals.org). Supplementary materials consist of data provided by the author that are published to benefit the reader. The posted materials are not copyedited. The contents of all supplementary data are the sole responsibility of the authors. Questions or messages regarding errors should be addressed to the author.