Fatal Pediatric Melioidosis and the Role of Hyperferritinemic Sepsis-Induced Multiple-Organ Dysfunction Syndrome

ABSTRACT.

Melioidosis is reported to cause a high fatality rate in children, even in the absence of risk factors for disease. The aim of this study was to identify characteristics of fatal pediatric melioidosis infection. We performed a retrospective analysis of children aged < 15 years with culture-confirmed melioidosis admitted to Bintulu Hospital in Sarawak, Malaysian Borneo, from January 2011 to December 2020. Forty-one children had culture-confirmed melioidosis. Nine (22%) had a fatal outcome; 8 (89%) had no predisposing risk factors. Bacteremia, septic shock, and acute respiratory distress syndrome were present in all fatalities. Demographic characteristics, presenting manifestation, and disseminated infection were not significantly associated with mortality, whereas the presence of splenomegaly, cytopenia, disseminated intravascular coagulation, and hepatobiliary dysfunction, all of which are features of hyperferritinemic sepsis-induced multiple-organ dysfunction syndrome, were associated with mortality. Hyperferritinemic sepsis-induced multiple-organ dysfunction syndrome may be a key component in the pathogenesis of fatal pediatric melioidosis.

Melioidosis, despite reported fatality rates of up to 40%,¹ is believed to be an opportunistic infection affecting adults with comorbidities and should rarely lead to mortality if early diagnosis, specific antimicrobial therapy, and intensive care are available.² In children, however, fatality rates of up to 24% have been reported despite absence of risk factors and provision of intensive care.³ Although delayed presentation and diagnosis could underlie these fatalities, the mechanisms and pathogenesis of severe disease remain unclear.

Hemophagocytosis has been documented in children and adults without comorbidities who succumbed to melioidosis,^4,5 suggesting hyperferritinemic sepsis-induced multiple-organ dysfunction syndrome (MODS; a secondary hemophagocytic lymphohistiocytosis [HLH] precipitated by infection) as a mechanism of life-threatening infection. Hyperferritinemic sepsis-induced MODS, like other forms of HLH, is classically diagnosed by the presence of five of eight criteria that include splenomegaly, cytopenia, hyperferritinemia, hypertriglyceridemia, hypofibrinogenemia, elevated soluble CD25, absent natural killer cytotoxic activity, and hemophagocytosis.⁶ Five of these criteria, however, represent investigations that are not routinely performed or are typically unavailable in resource-constrained regions. Recently, a simplified diagnostic criteria has been proposed based on a combination of hepatobiliary dysfunction (HBD) and disseminated intravascular coagulation (DIC).⁷ The aim of this study was to identify characteristics of fatal pediatric melioidosis and determine whether features of hyperferritinemic sepsis-induced MODS were present in these fatal infections.

We performed a retrospective descriptive analysis of children aged < 15 years admitted with culture-confirmed melioidosis over a 10-year period from January 2011 to December 2020. The study was conducted in Bintulu Hospital, a 302-bed hospital which provides medical, surgical, and intensive care services to a total population of 256,000, including 72,000 children aged < 15 years, residing in Bintulu Division and Belaga district of Kapit Division in Sarawak, Malaysian Borneo. This region in central Sarawak has been identified as a hotspot for melioidosis infections.^3,8

Culture-confirmed melioidosis was defined by isolation of Burkholderia pseudomallei from any clinical sample. To identify cases, we conducted a manual search of the microbiology laboratory logbooks and electronic database. Medical records of identified cases were retrieved and reviewed, and details were collected using a standardized case report form. The microbiological specimen collection and processing procedures have been described elsewhere.⁹ Clinical definitions used are shown in Table 1. Statistical analysis was performed using SPSS Statistics 21. The Mann-Whitney U test was used for continuous variables and Fisher’s exact test was used for categorical variables. The study was approved by the Malaysian Medical Research Ethics Committee (NMRR ID-21-02336-NEJ).

Table 1.

Clinical definitions used in this study of fatal pediatric melioidosis infections, Sarawak, Malaysia, 2011–2020

Term	Definition
Poor nutritional status	In children aged ≤ 10 years, poor nutritional status was diagnosed if weight-for-age was below –2 z-score using the WHO Child Growth Standards.10 Children aged > 10 years were considered to have poor nutritional status if their body weight was below the third percentile using the CDC weight-for-age percentiles.11
Primary site of infection	The initial infection site determined based on the initial organ-specific symptom.
Secondary site of infection	Infection site(s), established based on abnormal physical and/or radiological findings, which developed later or only became evident after hospital admission.
Localized disease	Presence of single, discrete, culture-positive focus of infection, in the absence of a positive blood culture and clinical/radiological evidence of dissemination to other sites.
Disseminated disease	Presence of infection in ≥ 2 discrete body sites and/or a positive blood culture.
Septic shock	Presence of hypotension (systolic blood pressure below the fifth percentile) with evidence of inadequate tissue perfusion unresponsive to fluid replacement.
Melioidosis-appropriate antibiotics	Use of either ceftazidime or a carbapenem during the intensive phase and oral trimethoprim-sulfamethoxazole during the eradication phase, with amoxicillin-clavulanate or doxycycline used as second-line oral agents when resistance, contraindications, or intolerance to trimethoprim-sulfamethoxazole was present.
Acute respiratory distress syndrome (ARDS)	According to the Pediatric Acute Lung Injury Consensus Conference Group,12 pediatric ARDS was defined in children without peri-natal related lung disease as respiratory failure evidenced by an acute deterioration in oxygenation, not fully explained by cardiac failure or fluid overload, occurring within 7 days of known clinical insult, with chest imaging findings of new infiltrates consistent with acute pulmonary parenchymal disease.
Cytopenia	Diagnosed if at least 2 cell lines were involved, with abnormal cell lines defined as a hemoglobin < 10 g/dL, leukocytes < 4.0 × 109 cells/L, and platelets < 100 × 109/L.
Disseminated intravascular coagulation (DIC)	Prothrombin time or partial thromboplastin time ≥ 1.2× normal value, with a platelet count ≤ 100 × 109/L or ≥ 50% decrease in platelet count.13
Hepatobiliary dysfunction (HBD)	Presence of two of three criteria: total serum bilirubin ≥ 43 μmol/L, serum aspartate aminotransferase or alanine aminotransferase ≥ 2× upper limit of normal, and/or prothrombin time ≥ 1.5× normal value.13
Acute kidney injury (AKI)	Fifty percent reduction of estimated creatinine clearance or urine output < 0.5 mL/kg/hour for at least 16 hours, according to the pediatric-modified RIFLE criteria.14

Forty-one children with culture-confirmed melioidosis were identified. Medical records of all cases were available for analysis. Nine (22%) had a fatal outcome. The median duration between admission and death was 2 days (interquartile range 1–7.5 days).

Key characteristics and outcomes are shown in Table 2. Thirteen (32%) children were aged < 5 years. Thirty-three percent (13/39) of children with data available had poor nutritional status, including 26% (8/31) of survivors and 63% (5/8) of nonsurvivors (P = 0.09). Only one (2%) child had a preexisting medical condition (diabetes mellitus). No significant demographic differences were found between survivors and nonsurvivors.

Table 2.

Characteristics and outcomes of 41 children with culture-confirmed melioidosis in Bintulu Hospital, Sarawak, Malaysia, 2011–2020

Characteristic	Total (N = 41)	Survivors (n = 32)	Nonsurvivors (n = 9)	P value
Demographics
Male sex	26 (63)	20 (63)	6 (67)	> 0.99
Age, years, median (IQR)	8.3 (2.7–10.9)	9.2 (2.4–11.0)	6.5 (5.4–9.0)	0.53
Poor nutritional status*	13 (33)	8 (26)	5 (63)	0.09
Preexisting medical conditions	1 (2)	0 (0)	1 (11)	0.22
Clinical manifestation
Time between onset and admission, days, median (IQR)	14 (8–26)	14 (8–30)	14 (6–14)	0.26
History of fever or fever on admission	37 (90)	28 (88)	9 (100)	0.56
Primary site of infection
Cervical lymph node disease	16 (39)	15 (47)	1 (11)	0.07
Fever without a source	11 (27)	7 (22)	4 (44)	0.22
Pneumonia	10 (24)	6 (19)	4 (44)	0.19
Hepatomegaly	17 (41)	10 (31)	7 (78)	0.02
Splenomegaly	6 (15)	1 (3)	5 (56)	0.001
Laboratory findings†
Hemoglobin, g/dL, median (IQR)	10.9 (9.9–12.4)	11.0 (10.3–12.4)	9.4 (8.9–12.3)	0.07
WBC, ×109 cells/L, median (IQR)	13.5 (7.1–17.1)	16.0 (11.9–18.7)	5.1 (2.2–6.4)	< 0.001
Platelet, ×109/L, median (IQR)	327 (222–453)	400 (283–511)	180 (122–223)	< 0.001
Sodium, mmol/L, median (IQR)	133 (130–138)	135 (131–138)	130 (123–133)	0.004
Urea, mmol/L, median (IQR)	2.9 (2.2–4.3)	2.6 (2.1–3.4)	5.0 (3.2–7.2)	0.008
Creatinine, μmol/L, median (IQR)	51 (41–71)	47 (41–69)	84 (40–124)	0.28
Total bilirubin, μmol/L, median (IQR)	9 (5–13)	8 (4–12)	13 (11–20)	0.02
Direct bilirubin, μmol/L, median (IQR)	5 (2–11)	4 (2–9)	11 (8–15)	0.02
AST, U/L, median (IQR)	72 (34–335)	46 (29–130)	399 (346–702)	< 0.001
ALT, U/L, median (IQR)	38 (17–103)	28 (13–76)	85 (81–193)	0.004
Albumin, g/L, median (IQR)	30 (24–38)	33 (27–39)	22 (20–25)	< 0.001
ESR, mm/hr, median (IQR)	78 (52–96)	82 (66–96)	69 (37–88)	0.32
Chest radiograph finding‡
Clear lung fields	19 (54)	18 (69)	1 (11)	0.005
Lobar/multilobar	9 (26)	6 (23)	3 (33)	0.67
Widespread opacities	7 (20)	2 (8)	5 (56)	0.006
Summary findings§
Disseminated disease	30 (73)	21 (66)	9 (100)	0.08
Number of organ sites involved
≥ 2 organ sites	25 (61)	17 (53)	8 (89)	0.07
≥ 3 organ sites	9 (22)	5 (16)	4 (44)	0.09
Secondary sites of infection¶
Spleen (abscesses)#	21 (55)	15 (50)	6 (75)	0.26
Lungs	8 (20)	3 (9)	5 (56)	0.007
Joints	5 (12)	2 (6)	3 (33)	0.06
Bacteremia	17 (41)	8 (25)	9 (100)	< 0.001
Septic shock	11 (27)	2 (6)	9 (100)	< 0.001
ARDS	11 (27)	2 (6)	9 (100)	< 0.001
Cytopenia	10 (24)	2 (6)	8 (89)	< 0.001
DIC	9 (22)	2 (6)	7 (78)	< 0.001
HBD**	8 (28)	3 (14)	5 (71)	0.008
Both DIC and HBD††	6 (15)	2 (6)	4 (50)	0.01
Acute kidney injury	6 (15)	0 (0)	6 (67)	< 0.001
Treatment
Melioidosis-appropriate antibiotic at admission	21 (51)	15 (47)	6 (67)	0.45
Intensive care unit admission	11 (27)	2 (6)	9 (100)	< 0.001
Mechanical ventilation	11 (27)	2 (6)	9 (100)	< 0.001
Inotropes/vasopressors	12 (29)	3 (9)	9 (100)	< 0.001
Renal replacement therapy	6 (15)	0 (0)	6 (67)	< 0.001

ALT = alanine aminotransferase; AST = aspartate aminotransferase; DIC = disseminated intravascular coagulation; ESR = erythrocyte sedimentation rate; HBD = hepatobiliary dysfunction; IQR = interquartile range; WBC = white blood cell count. Data are n (%) unless otherwise indicated.

^*Thirty-nine children (survivors, N = 31; nonsurvivors, N = 8) had nutritional status data available.

^†Only investigations done on the day of admission were included: 40 children had hemoglobin, WBC, platelet count, sodium, urea (survivors, n = 31; nonsurvivors, n = 9); 22 children had creatinine (survivors, n = 17; nonsurvivors, n = 5); 29 children had total bilirubin, direct bilirubin, AST, ALT, albumin (survivors, n = 22; nonsurvivors, n = 7); 28 children had ESR (survivors, n = 23; nonsurvivors, n = 5).

^‡In 35 children with chest radiography performed on the day of admission (survivors, n= 26; non-survivors, n = 9).

^§Includes clinical and laboratory findings obtained throughout the admission.

^¶In sites involved in ≥ 5 children.

# In 38 children with abdominal ultrasonography performed (survivors, n = 30; nonsurvivors, n = 8).

** In 29 children with liver function tests (survivors, n = 22; nonsurvivors, n = 7).

†† In 40 children with adequate laboratory investigations to confirm/exclude the presence of both DIC and HBD (survivors, n = 32; nonsurvivors, n = 8).

Cervical lymph node disease, fever without a source, and pneumonia were leading presentations, reported in 90% (37/41). Other presentations included skin/soft tissue abscess (N = 3) and parotid abscess (N = 1). The presenting manifestation was not significantly associated with mortality. In contrast, the presence of hepatomegaly and/or splenomegaly were associated with a fatal outcome (P = 0.02 for hepatomegaly and P = 0.001 for splenomegaly), as were widespread alveolar opacities on admission chest radiographs.

Overall, 73% (30/41) of patients had disseminated disease, and 41% (17/41) had bacteremia. Bacteremia, but not disseminated disease or number of affected organ-sites, was associated with mortality. Bacteremia was present in all fatal cases and in 25% (8/32) of survivors (P < 0.001), with a case fatality rate (CFR) of 53% (9/17). Septic shock occurred in all fatal cases as did acute respiratory distress syndrome (ARDS). Conversely, only 6% (2/32) of survivors had septic shock and/or ARDS (P < 0.001 for both septic shock and ARDS). The CFR was 82% (9/11) when septic shock and/or ARDS was present. The presence of cytopenia (89% [8/9] of fatal cases versus 6% [2/32] of survivors, odds ratio [OR] 120, 95% confidence interval [CI] 10–497; P < 0.001), DIC (78% [7/9] of fatal cases versus 6% [2/32] of survivors, OR 53, 95% CI 6–440; P < 0.001), and HBD (71% [5/7] of fatal cases versus 14% [3/22] of survivors, OR 16, 95% CI 2–122; P = 0.008) were all associated with mortality. Both DIC and HBD were present in 50% (4/8) of fatal cases with data available, compared with 6% (2/32) of survivors (OR 15, 95% CI 2–110; P = 0.01). Mortality was 67% (4/6) when both DIC and HBD were present compared with 0% (0/19) when neither was present.

Serum ferritin was evaluated in five children. In both fatal cases, the serum ferritin was markedly elevated: 6,692 ng/mL and > 2,000 ng/mL (and not further diluted). Three survivors had serum ferritin levels of 56 ng/mL, 96 ng/mL, and > 1,500 ng/mL (and not further diluted).

In the literature, few studies have evaluated risk factors for fatal pediatric melioidosis. In a previous study in Sarawak, we showed that bacteremia, disseminated disease, and presentation with undifferentiated fever predicted mortality.³ In Cambodia, children with pneumonia have higher mortality.¹⁵ In adults, underlying risk factors and older age are the most important predictors of death, as are pulmonary presentations.²

In this study, the primary site of infection was not significantly associated with mortality, and neither was disseminated disease. Although limited by the small sample size, this discrepancy with our previous findings may be explained by the increased use of abdominal ultrasonography which enabled the detection of occult splenic abscesses in children with negative blood cultures (and good outcomes), who would otherwise have been classified as having localized disease. These findings suggest that the primary site of infection and initial dissemination (e.g., to the spleen) may not be the dominant factors determining outcome. As in most melioidosis literature, however, the presence or development of bacteremia was strongly associated with mortality,¹ and once secondary lung involvement, septic shock, and ARDS occur, case fatality rates exceed 80%.

Hyperferritinemic sepsis-induced MODS may be an important driver of severe disease and poor outcomes in childhood melioidosis. The combination of DIC and HBD, a surrogate marker for hyperferritinemic sepsis-induced MODS,⁷ was found in 50% of our fatal cases and was associated with mortality in 67%. This was similar to the 64% mortality reported among children with DIC and HBD in a pediatric sepsis cohort with an overall CFR of 8%.¹⁶ Intriguingly, splenomegaly and cytopenia, both of which are major components of HLH diagnosis, were also present in most of our fatal cases. Marked hyperferritinemia was also found, although this was evaluated in only two (22%) fatal cases. Notably, although rare case reports of HLH complicating melioidosis in adults have been reported,^17,18 hyperferritinemic sepsis-induced MODS has not typically been described in association with mortality in adult melioidosis, and this may suggest a major difference in the possible immunopathogenesis of severe pediatric melioidosis compared with that of adult disease.

This study has several limitations. The small sample size has likely resulted in inadequate power to confirm some mortality associations. Because multivariable analysis was not performed, we could not rule out confounding factors. The retrospective nature of the study inevitably resulted in incomplete data, most notable in serum ferritin measurements. Furthermore, none of the cases were specifically investigated for the remaining HLH diagnostic criteria (e.g., serum triglycerides or fibrinogen), and familial HLH was not excluded. Nonetheless, the study identifies several previously unreported predictors of pediatric melioidosis mortality, including organomegaly, cytopenia, DIC, and HBD.

In conclusion, children in Sarawak, Malaysian Borneo, have a high melioidosis fatality rate despite absence of comorbidities and provision of intensive care. Hyperferritinemic sepsis-induced MODS may be a key component in the pathogenesis of severe infection. Community and health service delivery interventions that facilitate earlier presentation and diagnosis, before progression to secondary lung involvement, septic shock, and ARDS, will likely lead to better outcomes. Further studies to confirm the role of hyperferritinemic sepsis-induced MODS are urgently needed, as effective immunomodulatory therapies (e.g., corticosteroids, intravenous immunoglobulin, or plasma exchange) are available and may be beneficial in life-threatening infections.