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* Infectious Diseases Division
Pediatric Critical Care Division
Neonatology Division, Department of Pediatrics, University of British Columbia and British Columbias Childrens Hospital, Vancouver, British Columbia, Canada
|| National Microbiology Laboratory, Canadian Science Center for Human and Animal Health, Winnipeg, Manitoba, Canada
| ABSTRACT |
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Key Words: human metapneumovirus viral pneumonia prematurity respiratory failure ECMO mechanical ventilation
Abbreviations: hMPV, human metapneumovirus ECMO, extracorporeal membrane oxygenation PICU, pediatric intensive care unit RSV, respiratory syncytial virus CMV, cytomegalovirus PCR, polymerase chain reaction
Human metapneumovirus (hMPV) is a newly discovered cause of acute respiratory tract infection among children and adults that was first reported in the Netherlands.1 The spectrum of disease ranges from mild upper respiratory symptoms to severe lower respiratory tract disease with respiratory failure necessitating mechanical ventilation.1 To date, no reports of human patients requiring extracorporeal membrane oxygenation (ECMO) support for severe hMPV bronchiolitis or pneumonia have been published. We describe a premature infant from British Columbia, Canada, with hMPV-associated life-threatening pneumonia who required ECMO support for survival.
| CASE REPORT |
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This infant was born at 27 weeks of gestation (through cesarean section, because of preterm labor), with a birth weight of 1200 g and Apgar scores of 1 and 8 at 1 and 5 minutes, respectively. He developed hyaline membrane disease and had a persistently patent ductus arteriosus, which was treated with indomethacin. Mechanical ventilation was required for 3 weeks. The patient was discharged from the hospital at 2 months of age. Palivizumab was administered at 1 and 2 months of age, and the patient was scheduled to receive a third dose when he became ill. Routine immunizations were given at 2 months, except for pneumococcal conjugate vaccine (Prevnar; Wyeth Pharmaceuticals, Philadelphia, PA).
At the time of arrival at the local community hospital emergency department, the child was sick-looking, with an axillary temperature of 34.9°C, a heart rate of 140 beats per minute, and a respiratory rate of 30 breaths per minute. An intermittent dry cough was present. Bilateral pulmonary rales and decreased breath sounds were noted. Cardiac examination results were normal, but weak femoral pulses and mottled extremities were found. Repeated episodes of apnea led to endotracheal intubation and mechanical ventilation. Blood was taken for cultures, and cefotaxime and vancomycin were administered intravenously. Two boluses of normal saline solution were required to improve circulation. The initial complete blood count revealed a hemoglobin level of 11.4 g/dL, a leukocyte count of 6800 cells per mm3 (40% neutrophils, 56% lymphocytes, 3% monocytes, and 1% eosinophils), and a platelet count of 402 000 platelets per mm3. The C-reactive protein level, serum electrolyte levels, and urinalysis results were normal. An initial chest radiograph showed a diffuse, bilateral, interstitial infiltrate suggesting viral pneumonia, with no focal consolidations or effusions. The patient was transferred to the pediatric intensive care unit (PICU) at British Columbias Childrens Hospital.
Twenty-four hours after admission to the PICU, a repeat chest radiograph revealed bilateral patchy infiltrates involving the right upper and middle lobes and the left perihilar region, with areas of atelectasis in the right upper lobe. No pleural pathologic lesions or air leaks were visible. The patient received high-frequency oscillatory mechanical ventilation for 4 days, with no significant clinical or radiologic improvement. Nitric oxide was administered with no clinical effect, and dopamine was required for systemic blood pressure support. Serial chest radiographs revealed worsening bilateral infiltrates with air bronchograms (Fig 1). The results of an echocardiogram were normal except for a small patent ductus arteriosus. Respiratory failure progressed despite maximal conventional critical care support; by day 4, the child exhibited oxygen saturation values ranging from 77% to 88%, with hypercapnia, and the oxygenation index had increased from 13 to 26. An arterial blood gas analysis performed on the morning of day 4 of hospitalization showed a pH of 7.28, an arterial partial pressure of oxygen of 45 mm Hg, an arterial partial pressure of carbon dioxide of 82 mm Hg, and a bicarbonate level of 37 mEq/L. Diffuse, bilateral, pulmonary opacification was observed at that time. After discussion with the family, venovenous ECMO was initiated.
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| DISCUSSION |
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Lower respiratory tract infections that progress to respiratory failure and necessitate ECMO support are associated with increased morbidity and mortality rates. ECMO support has been used in the treatment of life-threatening infections caused by viruses, bacteria, fungi, mycobacteria, and atypical organisms.612 The success of this respiratory support mode has been variable, ranging from no effect to complete recovery. A key consideration is whether lung injury is reversible during the limited period in which ECMO support can be maintained. In this case, hMPV-induced lung injury resolved substantially during 10 days of lung rest with ECMO support.
Repeated tests for common causes of pneumonia were performed and yielded negative results. These tests for other common pathogens, including direct immunofluorescence tests for RSV, are sensitive and the results support hMPV as the etiologic agent in this case. The possible source of infection for this infant might have been 1 of his 3 sick household contacts, none of whom was screened for respiratory viruses. The patient did not meet the diagnostic criteria for severe acute respiratory syndrome and was not screened for it. To date, no pediatric cases of severe acute respiratory syndrome have been documented in British Columbia.
Reverse transcriptase-PCR has been used as the laboratory tool for diagnosis in the majority of hMPV studies. The detection of hMPV in this case may indicate only respiratory tract coinfection, rather than the real cause of pneumonia, but this seems unlikely, considering the epidemiologic, clinical, and laboratory evidence. Coinfection with other viral pathogens, including RSV, adenovirus, influenza A and B, and CMV, has been documented,5 but no evidence of such agents was obtained in this case, despite appropriate investigations. As recently noted, asymptomatic or subclinical hMPV infections seem to be rare, and the evidence to date suggests that hMPV is a causative agent of respiratory tract infections, especially among children <5 years of age.5,13,14 In reports to date, hMPV was recovered most commonly from nasopharyngeal aspirates and rarely from tracheal aspirates, but the optimal specimen for patients with hMPV pneumonia is unclear.
There is inadequate evidence to allow comments on prematurity as a risk factor for the development of severe hMPV pneumonia.4 Most adults have antibodies to hMPV.1 Infants lacking antibodies as a result of premature delivery may have greater difficulty coping with hMPV infection, like RSV infection.
| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Address correspondence to Rolando Ulloa-Gutierrez, MD, Pediatric Infectious Diseases Division, British Columbias Childrens Hospital, 4480 Oak St, Room K4-166, Vancouver, BC, Canada V6H 3V4. E-mail: rgut{at}cw.bc.ca
This work was presented in part as an abstract at the 4th Pediatric Infectious Diseases Society Conference; October 1214, 2003; Rancho Bernardo, California.
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