INTRODUCTION

Staphylococcus epidermidis(coagulase negative staphylococcus) is emerging as an increasingly important pathogen in the immunocompromised host. S. epidermi­dis has been isolated as an etiological agent in critical and life-threatening con­ditions such as septicemia in preterm infants (von Eiff et al. 2001). We report here a case of necrotizing pneumonia, rarely attributed to S.  epidermidis in a term infant who had earlier undergone surgical repair of tracheo-esophageal fistula.

CASE REPORT

A three-day old term male infant under­went end-to-end anastomosis and fistu­lectomy for esophageal atresia and tra­cheo-esophageal fistula.  Two days post-operatively, he was extubated, but devel­oped stridor and significant respiratory distress requiring re-ventilation. Several attempts at extubation failed; hence a bronchoscopic examination was per­formed at day 10, which revealed signifi­cant edema at the fistulectomy site (level of the third thoracic vertebra). He was commenced on a tapering course of dex­amethasone therapy over five days to facilitate extubation. However, on day 15 of life, he had evidence of sepsis and increased oxygen and ventilatory re­quirements. He was febrile (tempera­ture of 38o Celsius) and there were coarse crepitations on auscultation of both lung fields. A full blood count showed low total white cell number (1.4 X 109 /L) with neutropenia (0.9 X 109 /L) and thrombo­cytopenia (93 X 109 /L). Se­rum C-reactive protein (CRP) was also elevated (21 mg/dL). A chest radiograph showed ha­ziness of the right lung and multiple rounded radiolucent foci with no air-fluid levels (Figure 1). Ultrasono­graphic ex­amination of the lungs con­firmed areas of consolidation but there was no evidence of abscess or empyema formation. A ga­strograffin con­trast study did not reveal evidence of an anasto­motic leak. Cul­tures of blood, tra­cheal aspirates and the tip of the extra-pleural chest tube inserted intra-opera­tively grew coagulase nega­tive S. epi­dermidis. A diagnosis of S. epi­dermidis necrotizing pneumonia with septicemia was made and he was treated with intra­venous tei­coplanin and genta­micin for four weeks followed by two weeks of erythromycin. No percutaneous aspira­tion or pleural drainage was re­quired. A repeat chest radiograph after the first three weeks of treatment showed pneumatocele formation with some clearance of the pneumonia (Figure 2). The in­fant was success­fully extubated from mechanical ventila­tion to a brief pe­riod of continuous posi­tive air-way pres­sure support fol­lowed by nasal oxygen sup­plementation. The course of his hos­pital stay was not com­plicated by pneu­motho­rax or bron­cho­pleural fistula. The infant was dis­charged well after six weeks of antimi­crobial ther­apy. Complete radio­graphic resolution of the pneumoto­celes was seen on follow-up six months later.

DISCUSSION

Necrotizing pneumonia or pulmonary gangrene is a severe complication of bacterial pneumonia. More commonly reported in adults, this condition is rare in children and even more so among neo­nates. Organisms causing this cavitating form of pneumonia include Streptococcus pneumoniae, Streptococcus pyogenes, Mycoplasma pneumoniae(Hacimusta­faoglu et al. 2004), Pseudomonas aeru­ginosa (Reich 1993) and methicillin-re­sistant Staphyloccus aureus (McAdams et al. 2005). An exaggerated inflamma­tory response is present as evidenced by raised markers of inflammation such as CRP. The mortality rate has been re­ported to be as high as 5.5% (Hacimus­tafaoglu et al. 2004). Unlike lung ab­scess, which is usually a solitary cavity showing rim enhancement and an air-fluid level on plain radiography or CT scan, necrotizing pneumonia manifests as multiple radiolucent foci (air crescent sign) that may be replaced by pneumato­celes after the pneumonia (Hoffer et al. 1999). The underlying pathological pro-
cess involves ischemic necrosis due to vascular invasion by the organism with endarteritis causing nonviable or gan­grenous lung tissue to separate from the parenchyma (Reich 1993), creating rims of lucency (Yella et al. 2005) and subse­quently pneumatoceles as radiological findings (Hacimustafaoglu et al. 2004).

This is the first reported case of necro­tizing pneumonia caused by S. epidermi­dis in a neonate. We speculate that the invasiveness of this organism was heightened by the presence of risk fac­tors such as an extrapleural catheter and the institution of steroid therapy. Early recognition of necrotizing pneumonia in a high risk infant presenting with cavitating lung lesions is important for rapid institu­tion of optimal therapy to achieve a fa­vorable outcome. In this case, aggressive antimicrobial therapy as conservative management instead of invasive percu­taneous aspiration or drainage, resulted in complete resolution and avoided com­plications such as pneumothorax and bronchopleural fistula.