ABSTRACT.
Dengue is the most common mosquito-borne viral disease in humans. Although many dengue virus (DENV) infections are asymptomatic or produce only mild illness, DENV can occasionally cause severe and fatal disease. In this study, we compared the severity of primary and secondary DENV-1 infections among patients enrolled in a prospective, hospital-based, acute febrile illnesses surveillance system in Puerto Rico (2012–2014). Serum samples collected <7 days after symptom onset were tested for DENV-serotypes by a real time-polymerase chain reaction assay. The positive samples that were collected ≤5 days after onset were then tested by a DENV IgG antibody ELISA to classify primary (IgG negative) and secondary (IgG positive) infections. Overall, 720 dengue infections (679 DENV-1, 3 DENV-2, and 38 DENV-4) were diagnosed during the study period. Of the 679 DENV-1 patients, 595 were included in the study, 445 (75%) were classified as secondary infections, and 150 (25%) as primary infections. Among these patients, 150 (25%) were classified as severe dengue. Severe dengue occurred in 28% of secondary DENV-1 infections. Severe disease was also common among primary DENV-1 infections, including 27% with plasma leakage, 15% with severe dengue, and 9% requiring admission to the intensive care unit. Even though DENV-1 has caused thousands of cases in Puerto Rico, this is the first report describing DENV-1 as the cause of severe primary infection in this country. Although secondary DENV-1 infections have an increased risk for severe disease, it is important for clinicians to be aware that any individual with dengue should be considered at risk for severe dengue.
INTRODUCTION
Dengue is the most common arbovirus worldwide, with an 8-fold increase in incidence over the last two decades. Approximately half of the world population is at risk for infection, and dengue causes an estimated 40,000 deaths annually.1–3 Although most dengue virus (DENV) infections are asymptomatic or present with mild symptoms, dengue can lead to severe illness and death.3–5 Dengue is caused by four DENVs or serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) that share approximately 65% of their genomes; however, even within a single serotype, there can be marked genetic variation.6 Infection by one DENV serotype provides long-lasting protection against infection by the same serotype. However, heterotypic IgG antibodies, which confer short-term cross-protection against other DENV serotypes, decrease over time and are unable to effectively neutralize the virus in a subsequent infection, facilitating viral entry into cells and increasing the viral load, cytokine release, and vascular permeability.7–9 This phenomenon, called antibody-dependent enhancement (ADE), may lead to plasma leakage and is thought to be responsible for an increased risk of severe disease in secondary infections.7–9
Although all DENV serotypes can cause severe disease, differences in the severity and case fatality rates during outbreaks and evidence from immunological studies revealed that some DENV serotypes were associated more frequently with severe disease.10–12 DENV-2 has classically been associated with more severe disease, but a recent meta-analysis suggests that primary infections with DENV-3 were associated with higher risk for severe disease in South East Asia (SEA).13 Although that debate considered the severity of DENV-2 and DENV-3, more recently published meta-analysis indicated that only a few studies have focused on the potential severity of DENV-1 in Latin American countries.11,13
Since the 1960s, dengue has been a cause of morbidity in Puerto Rico, with epidemics occurring about every 3–5 years.9 More recently, the devastating burden of this disease included a total of 39,094 dengue cases that were reported from 2010 to 2024 to the Puerto Rico Department of Health in San Juan.14 The last major epidemic occurred during 2012–2014 when more than 30,000 suspected dengue cases were reported, of which 16,000 had diagnostic evidence of DENV infection.
A study conducted during the dengue epidemic in 2012–2014 indicated that most, including severe cases, were caused by DENV-1. However, a critical question that was not addressed was whether this virus caused primary and/or secondary infections, which could lead to severe disease.9 Therefore, the aim of this study was to determine if DENV-1 was the cause of severe primary and/or secondary infections, and to compare the clinical manifestations of the severe primary and secondary infections.
MATERIALS AND METHODS
To assess the severity and compare the clinical manifestations of primary and secondary DENV-1 infections, we performed a more detailed analysis of the results of a previously described group of patients with confirmed dengue in Puerto Rico from 2012 to 2014. The patients were recruited through the Sentinel Enhanced Dengue Surveillance System (SEDSS) program in Puerto Rico.9 SEDSS is a prospective, hospital-based, acute febrile illnesses surveillance system that operates in two hospitals in southern Puerto Rico: Saint Luke’s Episcopal Hospital located in Ponce (SLEH-Ponce), and SLEH-Guayama.9 Briefly, patients presenting to the emergency room with current or reported fever in the previous 7 days were invited to participate. Serum samples collected <7 days after symptom onset were tested by DENV-serotype-specific real time-polymerase chain reaction15; positive samples collected ≤5 days after onset were then tested by anti-DENV IgG ELISA.16 IgG results were used to classify primary (IgG negative) and secondary (IgG positive) DENV infections.9,16 Although the clinical presentation of the entire cohort was already published, severity by DENV serotype and immune status was not analyzed.9 For this post-hoc analysis, only DENV-1 cases, the most prevalent serotype which accounted for 94.1% of cases,9 with information about their DENV immune status were included.
Clinical and laboratory data were collected at presentation, during hospitalization, and 7–10 days after discharge. Information about clinical variables and disease severity was collected and compared between primary and secondary DENV-1 infections. Outcomes evaluated included: the 2009 WHO definition for severe dengue and dengue with warning signs,17 the 1997 WHO definition for dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS),18 plasma leakage, shock, thrombocytopenia (<100,000 platelets/mm3), hospitalization, admission to an intensive care unit (ICU), treatments received, and death.
Proportions were compared between groups by χ2 test and Fisher’s exact test and medians by Wilcoxon rank sum tests, respectively. Multivariable regression models that included age, gender, and comorbidities were used to estimate adjusted odds ratios (aORs) for severe outcomes in secondary DENV-1 infections (using primary DENV-1 infections as reference).
The SEDSS protocol was reviewed and approved by the Ponce Medical School Foundation, Inc. Institutional Review Board (#120308-VR/2311173707). Informed consent was given by all study participants.9
RESULTS
Overall, 720 dengue infections (679 DENV-1, 3 DENV-2, and 38 DENV-4) were diagnosed during the study period; 281 (39%) were classified as severe dengue. Because of the lack of immune status characterization (insufficient sample or timing of collection), 84 DENV-1 infections were excluded from the analysis. Among 595 patients with DENV-1 infection included in the study, 445 (75%) were classified as secondary DENV infections and 150 (25%) as primary infections; 150 (25%) were classified as severe dengue. Table 1 shows the comparison of patient characteristics, clinical presentations, and severity between primary and secondary DENV-1 infections.
Table 1.
Demographic characteristics, clinical findings at presentation, and severity classification of dengue among SEDSS patients with primary and secondary DENV-1 infections
| Patients’ Characteristics | Primary Infection (n = 150) | Secondary Infection (n = 445) | P-Value* | aOR (95% CI) |
|---|---|---|---|---|
| Baseline characteristics | ||||
| Gender, female | 63 (42.0) | 199 (44.7) | 0.628 | – |
| Age (years) | ||||
| 0–9 | 63 (42.0) | 83 (18.7) | <0.001 | – |
| 10–19 | 72 (48.0) | 215 (48.3) | >0.999 | – |
| 20–29 | 11 (7.3) | 54 (12.1) | 0.139 | – |
| ≥30 | 4 (2.7) | 93 (20.9) | <0.001 | – |
| Comorbidities | ||||
| Any chronic medical condition | 36 (24.0) | 135 (30.3) | 0.168 | – |
| Diabetes mellitus | 6 (4.0) | 27 (6.1) | 0.453 | – |
| High blood pressure | 2 (1.3) | 33 (7.4) | 0.011 | – |
| Dyslipidemia | 1 (0.7) | 18 (4.0) | 0.077 | – |
| Coronary heart disease | 0 | 16 (3.6) | 0.039 | – |
| Asthma | 26 (17.3) | 82 (18.4) | 0.859 | – |
| Neoplasm | 0 | 7 (1.6) | 0.268 | – |
| Clinical presentation | ||||
| Days post-illness onset, median (IQR) | 3 (0–7) | 3 (0–5) | 0.105 | – |
| 2009 WHO definition of dengue† | 123 (82.0) | 419 (94.2) | <0.001 | 2.8 (1.5–5.2) |
| Fever | 150 (100) | 445 (100) | – | – |
| Nausea/vomiting | 91 (62.3) | 329 (74.4) | 0.007 | 1.5 (1.0–2.2) |
| Rash | 90 (61.2) | 233 (53.3) | 0.116 | 0.8 (0.6–1.3) |
| Headache | 112 (74.7) | 392 (88.1) | <0.001 | 1.9 (1.1–3.2) |
| Retro-orbital pain | 78 (54.2) | 288 (65.5) | 0.020 | 1.3 (0.8–1.9) |
| Muscle/bone/back pain | 94 (65.3) | 359 (81.4) | <0.001 | 1.6 (1.0–2.4) |
| Joint pain | 70 (49.3) | 279 (63.6) | 0.004 | 1.3 (0.9–1.9) |
| Jaundice | 2 (1.4) | 23 (5.2) | 0.082 | 4.5 (1.2–28.9) |
| Any dengue warning sign | 94 (62.7) | 324 (72.8) | 0.025 | 1.5 (1.0–2.3) |
| Laboratory parameters | ||||
| AST or ALT (>50 IU/L) | 54 (73.0) | 201 (85.2) | 0.026 | 2.1 (1.1–4.1) |
| AST or ALT (>1,000 IU/L) | 2 (2.7) | 7 (3.0) | >0.999 | 1.0 (0.2–6.9) |
| PT INR >1.5 | 0 | 3 (11.5) | >0.999 | – |
| Leukopenia (WBC <4,000 × 103 cells) | 93 (64.1) | 292 (67.0) | 0.600 | 1.0 (0.7–1.6) |
| Thrombocytopenia (platelets <100,000) | 51 (35.4) | 199 (45.6) | 0.040 | 1.4 (0.9–2.1) |
| Thrombocytopenia (platelets <50,000) | 16 (28.6) | 81 (41.1) | 0.122 | 1.4 (0.7–1.6) |
| Hypoalbuminemia‡ | 34 (54.0) | 139 (71.3) | 0.017 | 2.1 (1.1–4.0) |
| 2009 WHO dengue severity classification | ||||
| Dengue (nonsevere) | 127 (84.7) | 322 (72.4) | 0.004 | 0.5 (0.3–0.8) |
| Without warning signs | 53 (41.7) | 104 (32.3) | 0.075 | 0.7 (0.5–1.1) |
| With warning signs | 74 (58.3) | 218 (67.7) | 0.075 | 1.4 (0.9–2.2) |
| Severe dengue | 23 (15.3) | 123 (27.6) | 0.004 | 2.1 (1.3–3.5) |
| Without warning signs | 3 (13.0) | 17 (13.8) | 1.000 | 1.0 (0.3–4.7) |
| With warning signs | 20 (87.0) | 106 (86.2) | 1.000 | 1.0 (0.2–3.7) |
| Severe plasma leakage or shock | 18 (12.0) | 88 (19.8) | 0.043 | 1.7 (1.0–3.1) |
| Severe bleeding | 9 (6.2) | 41 (9.3) | 0.322 | 1.6 (0.8–3.7) |
| Severe organ involvement | 2 (2.6)§ | 16 (6.7)‖ | 0.280 | 2.5 (0.7–16.1) |
| 1997 WHO definition for dengue hemorrhagic fever/dengue shock syndrome | ||||
| Any grade of DHF/DSS¶ | 22 (15.4) | 75 (17.2) | 0.699 | 1.1 (0.7–2.0) |
| DHF I/II | 19 (13.3) | 64 (14.7) | 0.776 | 1.1 (0.6–2.0) |
| DHF III/IV (=DSS) | 3 (2.2) | 11 (2.6) | >0.999 | 1.1 (0.3–5.2) |
| Warning signs# | ||||
| Mucosal bleeding | 13 (8.9) | 56 (12.6) | 0.285 | 1.4 (0.7–2.7) |
| Abdominal pain | 84 (57.9) | 287 (65.2) | 0.138 | 1.3 (0.9–2.0) |
| Vomiting (≥3 episodes per day) | 43 (29.3) | 124 (28.2) | 0.886 | 0.9 (0.6–1.4) |
| Lethargy | 38 (26.0) | 160 (36.9) | 0.022 | 1.4 (0.9–2.1) |
| Hemoconcentration** | 7 (4.8) | 25 (5.7) | 0.843 | 0.9 (0.4–2.5) |
| Fluid accumulation (ascites, pleural effusion) | 3 (4.1) | 8 (3.5) | >0.999 | 0.7 (0.2–3.6) |
| Severe plasma leakage and shock | ||||
| Severe plasma leakage (plasma leakage + respiratory distress) | 17 (11.3) | 83 (18.7) | 0.052 | 1.8 (1.0–3.2) |
| Plasma leakage | 39 (26.9) | 152 (34.6) | 0.106 | 1.4 (0.9–2.2) |
| Respiratory distress†† | 52 (34.9) | 222 (51.3) | 0.001 | 1.8 (1.2–2.7) |
| Shock | 2 (1.3) | 7 (1.6) | >0.999 | 1.1 (0.2–7.6) |
| Any sign of poor circulation | 85 (56.7) | 309 (69.4) | 0.006 | 1.5 (1.0–2.2) |
| ≥2 signs of poor circulation | 24 (16.0) | 109 (24.5) | 0.041 | 1.4 (0.8–2.3) |
| Hospitalization/interventions | ||||
| Hospitalized | 58 (38.7) | 193 (43.4) | 0.361 | 1.3 (0.9–1.9) |
| Length of hospital stay, median (IQR) | 4 (2.0–11.0) | 3 (0.0–10.0) | 0.058 | – |
| Admitted to an ICU (among hospitalized) | 5 (8.8) | 10 (5.2) | 0.505 | 0.7 (0.2–2.2) |
| Any blood product received (among hospitalized) | 2 (3.5) | 6 (3.1) | >0.999 | 0.7 (0.1–5.1) |
| Oxygen (among hospitalized) | 4 (7.1) | 3 (1.6) | 0.080 | 0.2 (0–0.9) |
| Intubation | 0 | 0 | – | – |
| Use of vasopressors | 0 | 0 | – | – |
| Death | 0 | 1 (0.2) | >0.999 | – |
ALT = alanine aminotransferase; aOR = adjusted odds ratio; AST = aspartate aminotransferase; DHF/DSS = dengue hemorrhagic fever/dengue shock syndrome; ICU = intensive care unit; IQR = interquartile range; PT INR = prothrombin time international normalized ratio; SD = severe dengue; SEDSS = Sentinel Enhanced Dengue Surveillance System; WBC = white blood cells. Ponce, Puerto Rico, 2012–2014. Significant findings are shown in bold.
Proportions between groups were compared using χ2 and Fisher’s exact test. Medians were compared by Mann-Whitney rank sum test.
2009 WHO definition for probable dengue included the presence of fever and at least two of the following criteria: nausea/vomiting, rash, pains or aches, leukopenia, or any warning sign. The presence of a positive tourniquet test was not considered because it was not systemically measured in this study.
Hypoalbuminemia was defined as low albumin adjusted for age.
Severe organ involvement in primary dengue virus-1 infections (2): aspartate aminotransferase or alanine aminotransferase ≥1,000 IU/L (2).
Severe organ involvement in secondary dengue virus-1 infections (16): aspartate aminotransferase or alanine aminotransferase ≥1,000 IU/L (9), encephalitis (5), prothrombin time international normalized ratio ≥1.5 (3).
DHF/DSS: all cases were DHF, no patient presented with DSS.
Hepatomegaly and restlessness were not considered because they were not systematically measured in this study.
Hemoconcentration was defined as a hematocrit change >20% during illness or a hematocrit >20% above baseline for age and gender at any time during illness.
Respiratory distress was defined as tachypnea (respiratory rate >20 revolutions per minute), need for oxygen, or intubation.
Overall, 262 (44%) dengue cases were female. Secondary DENV-1 cases were older (median age 16 versus 11 years, P <0.001) and had a higher prevalence of chronic medical conditions such as hypertension (7% versus 1%, P = 0.011) and chronic heart disease (4% versus 0, P = 0.039). Secondary DENV-1 cases were more likely to meet the 2009 WHO dengue case definition than primary cases (94% versus 82%, P <0.001). Elevated transaminases (>50 IU/L, 85% versus 73%, P = 0.026), thrombocytopenia (platelets <100,000, 46% versus 35%, P = 0.040), and hypoalbuminemia (71% versus 54%, P = 0.017) were more common in secondary DENV-1 infections.
The proportion of cases with warning signs was higher in secondary infections (73% versus 63%, P = 0.003). Patients with secondary infections developed severe dengue in 28% of cases compared with 15% of patients with primary infections (P = 0.004). The use of warning signs to predict progression to severe dengue also differed by infection status, with 21% (20 of 94) of patients with warning signs progressing to severe dengue on the primary infection, compared with 33% (106 of 324) on the secondary infection (P = 0.045). No significant differences were seen in the risk for developing severe dengue among patients without warning signs, with 2% (3 of 56) of patients without warning signs developing severe dengue on primary infection, and 14% (17 of 121) of patients on secondary infection (P = 0.149). The difference in progression to severe dengue was mainly because of the presence of severe plasma leakage or shock (20% in secondary infections versus 12% in primary infections, P = 0.043). Severe bleeding and severe organ involvement occurred in 9% and 7% of patients with secondary infection, respectively, and in 6% and 3% of patients with primary infection (P = 0.322 and P = 0.280). When applying the 1997 case definitions, DHF and DSS did not differ between groups (17% in secondary infection versus 15% in primary infection, P >0.999).
Overall, 42% of dengue patients were admitted to the hospital, and 6% of hospitalized patients were admitted to ICUs. There were no significant differences in hospitalization rates, admission to ICU, or length of stay between primary and secondary infections. The only fatal case occurred in a secondary DENV-1 infection.
After adjusting for age, gender, and relevant comorbidities, secondary DENV-1 infections were more likely to: meet the 2009 definition of dengue (aOR 2.8, 95% CI 1.5–5.2), and have severe dengue (aOR 2.1, 95% CI 1.3–3.5), severe plasma leakage (aOR 1.8, 95% CI 1.0–3.2), and jaundice (aOR 4.5, 95% CI 1.2–28.9) compared with primary DENV-1 infections (Table 1).
DISCUSSION
The present study was an extension of the study published by Paz-Bailey et al.9 describing severe primary and secondary DENV infections as a cause of severe dengue disease in Puerto Rico. Our study found that severe dengue cases were more common in secondary DENV-1 infections, occurring in 28% of cases. Notwithstanding, a considerable proportion (15%) of primary DENV-1 infections were also severe, 12% developed severe plasma leakage and shock, and almost 10% required admission to ICU.
These observations were consistent with many studies that have demonstrated the severity of DENV infection varied depending on the circulating serotype and immune status, and that both secondary and primary DENV infections can cause severe dengue.13,19–23 Very little is known about the underlying mechanisms of severe primary DENV infections because ADE and subsequent plasma leakage only explain the increased severity of secondary DENV infections.8,9 Other factors, such as a higher inoculum, different viral strains, serotype or strain replacement, residual immunity or cross-protection to other serotypes or strains, and genetic variations in the host’s immune response, may also play a role.9,24
An understanding of how dengue severity is modulated by serotype and by primary and secondary infections is critical for public health policymakers. Although several studies have been conducted to address this question using the 1997 WHO severity classification, only a few studies have used the more relevant 2009 WHO definitions for severe dengue.13,23 In spite of this limitation, these studies showed that both DENV-2 and DENV-3 were associated with the greatest clinical severity. However, DENV-2 has traditionally been considered the most virulent DENV serotype.25 A recent meta-analysis showed that children infected with DENV-2 had a higher risk of developing severe disease than those infected with DENV-1 (OR 1.8) or DENV-3 (OR 2.2), but these risks were not adjusted for patients’ immune status.11 Another recent meta-analysis concluded that DENV-3 from SEA region displayed the greatest percentage of severe cases in primary infections (42%; 95% CI: 31–54%) compared with all other DENV serotypes from SEA and non-SEA regions; but no studies with DENV-1 from the non-SEA region were included in the meta-analysis.13 An analysis of a hospital-based study in Nicaragua also showed that the frequency of shock and hemorrhage among DENV-2 patients was higher when compared with DENV-1 cases.23 Our study showed a relatively high prevalence of severe disease in both primary and secondary infections caused by DENV-1 among symptomatic dengue cases seeking care at an emergency room. However, the lack of cases from other DENV serotypes, particularly for primary DENV infections, did not allow comparisons of dengue severity between serotypes. Although some information is emerging, an understanding of how the severity of dengue varies by serotype and immune status remains limited, especially in Latin America compared with regions like SEA.13,23
One limitation of our study is the exclusion of 12% of DENV-1 cases because of the lack of immune status characterization, which could lead to a possible selection bias. In our study, secondary DENV was defined by the presence of IgG during the acute phase of DENV infection. Therefore, we could not differentiate between secondary and postsecondary DENV infections, and the severity of secondary infections might be underestimated. The test sensitivity for detecting secondary infections could also be a contributing factor. Although, ELISA tests demonstrated better diagnostic performance than immunofluorescence assays, serological tests have shown suboptimal sensitivity for the identification of secondary DENV infections, particularly in patients with only one previous dengue episode, which are the patients at higher risk of severe disease.17,26 Patients with secondary infections but with low antibody titers could be misclassified as primary infections, increasing the proportion of severe cases in this group. Interestingly, a recent study found higher preexisting IgG titers among DENV-2 cases with warning signs, severe dengue, and DHF/DSS, compared with other serotypes.12 The authors also demonstrated that previous Zika infection was a risk factor for severe dengue.12 However, our cases occurred before the introduction of Zika in Puerto Rico, making previous Zika exposure very unlikely in our cohort.
Finally, most studies on dengue are conducted in low- and middle-income, dengue-endemic countries with limited surveillance resources. In contrast, Puerto Rico has a strong dengue surveillance system, and the SEDSS platform is based on detailed report forms, trained personnel, easy access to diagnostic tools, and highly specialized reference laboratory testing. This could lead to higher levels of detection of some warning signs or criteria for severe dengue, and explain the relatively high proportion of severe dengue among primary DENV-1 infections reported in our study. Moreover, patients included in the study were recruited at emergency rooms, potentially overestimating the proportion of severe dengue.
CONCLUSION
Although DENV has been documented as a cause of human disease at least since the 1960s in Puerto Rico, the findings of this study documented for the first time that primary DENV-1 infections were the cause of severe disease. It is important for clinicians to be aware that any individual with dengue should be considered at risk for severe dengue. Therefore, training on early identification of warning signs and signs of severe dengue are crucial to guide the management of dengue patients, regardless of the patient’s immune status. The clinical manifestations of the DENV-1 severe primary infections were similar to those associated with DENV-1 severe secondary infections, thus, demonstrating that severe dengue was caused by both primary and secondary DENV-1 infections during the epidemic of dengue from 2012–2014 in Puerto Rico. These findings underscore the critical need for a balanced dengue vaccine that offers protection against disease caused by all four DENV serotypes, especially (because both the more recent Dengvaxia and Qdenga vaccines show variable efficacy by DENV serotype)27,28 and are effective for both dengue-immune and dengue-naive individuals. Furthermore, our research observations further emphasize the global need for effective treatment strategies to manage and mitigate the global burden of dengue disease.
REFERENCES
- 1.WHO, 2024. Dengue and Severe Dengue. Available at: www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue. Accessed May 5, 2025.
- 2.Zeng Z, Zhan J, Chen L, Chen H, Cheng S, 2021. Global, regional, and national dengue burden from 1990 to 2017: A systematic analysis based on the global burden of disease study 2017. EClinicalMedicine 32: 100712. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Guzman MG, Harris E, 2015. Dengue. Lancet 385: 453–465. [DOI] [PubMed] [Google Scholar]
- 4.Kabra SK, Verma IC, Arora NK, Jain Y, Kalra V, 1992. Dengue hemorrhagic fever in children in Delhi. Bull World Health Organ 70: 105–108. [PMC free article] [PubMed] [Google Scholar]
- 5.Kalayanarooj S, 1999. Standardized clinical management: Evidence of reduction of dengue haemorrhagic fever case-fatality rate in Thailand. Dengue Bulletin 23: 10–17. [Google Scholar]
- 6.Lisova O, Belkadi L, Bedouelle H, 2014. Direct and indirect interactions in the recognition between a cross-neutralizing antibody and the four serotypes of dengue virus. J Mol Recognit 27: 205–214. [DOI] [PubMed] [Google Scholar]
- 7.Guzman MG, Alvarez M, Halstead SB, 2013. Secondary infection as a risk factor for dengue hemorrhagic fever/dengue shock syndrome: A historical perspective and role of antibody-dependent enhancement of infection. Arch Virol 158: 1445–1459. [DOI] [PubMed] [Google Scholar]
- 8.Katzelnick LC, Gresh L, Halloran ME, Mercado JC, Kuan G, Gordon A, Balmaseda A, Harris E, 2017. Antibody-dependent enhancement of severe dengue disease in humans. Science 358: 929–932. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Paz-Bailey G. et al. , 2022. Predominance of severe plasma leakage in pediatric patients with severe dengue in Puerto Rico. J Infect Dis 226: 1949–1958. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Nisalak A. et al. , 2016. Forty years of dengue surveillance at a tertiary pediatric hospital in Bangkok, Thailand, 1973–2012. Am J Trop Med Hyg 94: 1342–1347. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Sangkaew S, Ming D, Boonyasiri A, Honeyford K, Kalayanarooj S, Yacoub S, Dorigatti I, Holmes A, 2021. Risk predictors of progression to severe disease during the febrile phase of dengue: A systematic review and meta-analysis. Lancet Infect Dis 21: 1014–1026. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Katzelnick LC. et al. , 2020. Zika virus infection enhances future risk of severe dengue disease. Science 369: 1123–1128. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Soo K-M, Khalid B, Ching S-M, Chee H-Y, 2016. Meta-analysis of dengue severity during infection by different dengue virus serotypes in primary and secondary infections. PLoS ONE 11: e0154760. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Rodriguez DM, Madewell ZJ, Torres JM, Rivera A, Wong JM, Santiago GA, Rivera-Amill V, Paz-Bailey G, Marzan-Rodriguez M, Adams LE, 2024. Epidemiology of dengue—Puerto Rico, 2010–2024. MMWR Morb Mortal Wkly Rep 73: 1112–1117. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Santiago GA, Vergne E, Quiles Y, Cosme J, Vazquez J, Medina JF, Medina F, Colón C, Margolis H, Muñoz-Jordán JL, 2013. Analytical and clinical performance of the CDC real time RT-PCR assay for detection and typing of dengue virus. PLoS Negl Trop Dis 7: e2311. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Miagostovich MP, Noriega RM, dos Santos FB, Schatzmayr HG, Araujo ES, Vorndam V, 1999. Evaluation of an IgG enzyme-linked immunosorbent assay for dengue diagnosis. J Clin Virol 14: 183–189. [DOI] [PubMed] [Google Scholar]
- 17.WHO, 2009. Dengue Hemorrhagic Fever: Diagnosis, Treatment, Prevention and Control. Geneva, Switzerland: World Health Organization. [Google Scholar]
- 18.WHO, 1997. Dengue Hemorrhagic Fever: Diagnosis, Treatment, Prevention and Control. 2nd ed. Geneva, Switzerland: World Health Organization. [Google Scholar]
- 19.Rosen L, 1977. The Emperor’s New Clothes revisited, or reflections on the pathogenesis of dengue hemorrhagic fever. Am J Trop Med Hyg 26: 337–343. [DOI] [PubMed] [Google Scholar]
- 20.Aggarwal C. et al. , 2024. Severe disease during both primary and secondary dengue virus infections in pediatric populations. Nat Med 30: 670–674. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Huits R, Schwartz E, 2021. Fatal outcomes of imported dengue fever in adult travelers from non-endemic areas are associated with primary infections. J Travel Med 28: taab020. [DOI] [PubMed] [Google Scholar]
- 22.Anantapreecha S, Chanama S, A-Nuegoonpipat A, Naemkhunthot S, Sa-Ngasang A, Sawanpanyalert P, Kurane I, 2005. Serological and virological features of dengue fever and dengue hemorrhagic fever in Thailand from 1999 to 2002. Epidemiol Infect 133: 503–507. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Narvaez F. et al. , 2025. Dengue severity by serotype and immune status in 19 years of pediatric clinical studies in Nicaragua. PLoS Negl Trop Dis 19: e0012811. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Pare G. et al. ; Dengue Population Genetics Program, 2020. Genetic risk for dengue hemorrhagic fever and dengue fever in multiple ancestries. EBioMedicine 51: 102584. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Guzmán MG, Kourí G, Valdés L, Bravo J, Vázquez S, Halstead SB, 2002. Enhanced severity of secondary dengue-2 infections: Death rates in 1981 and 1997 Cuban outbreaks. Rev Panam Salud Publica 11: 223–227. [DOI] [PubMed] [Google Scholar]
- 26.Lopez AL. et al. , 2021. Determining dengue virus serostatus by indirect IgG ELISA compared with focus reduction neutralization test in children in Cebu, Philippines: A prospective population-based study. Lancet Glob Health 9: e44–e51. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Yang Y, Meng Y, Halloran ME, Longini IM, 2018. Dependency of vaccine efficacy on preexposure and age: A closer look at a tetravalent dengue vaccine. Clin Infect Dis 66: 178–184. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Rivera L. et al. , 2022. Three-year efficacy and safety of Takeda’s dengue vaccine candidate (TAK-003). Clin Infect Dis 75: 107–117. [DOI] [PMC free article] [PubMed] [Google Scholar]