Gemella morbillorum as a source bacteria for necrotising fasciitis of the torso

Abstract

A 66-year-old man presented with upper back cellulitis and imaging findings consistent with a necrotising soft tissue infection. He was started on broad-spectrum intravenous antibiotics and was taken to the operating room for immediate surgical debridement. On postoperative day 5, the culture was noted to be growing Gemella morbillorum, an exceedingly rare cause of necrotising soft tissue infections in immunocompetent hosts. His condition improved, and he was transitioned to oral antibiotics and discharged home.

Background

Gemella morbillorum, formerly known as Streptococcus morbillorum until 1988,¹ is part of the normal flora of the respiratory, urinary and gastrointestinal tracts in humans.² It is an uncommon cause of infection; however, there are case reports in the literature implicating this organism in serious and fatal infections.^2–6 Most of these reports are from endocarditis but other organs have also been affected, especially in immunocompromised patients. There are a few cases of necrotising fasciitis caused by G. morbillorum.^{7 8} We present a case of this uncommon disease.

Case presentation

A 66-year-old man with a medical history of hypertension and atrial fibrillation presented to the emergency department (ED) with a right upper back tender mass, surrounding erythema and associated fever. Prior to his presentation, he had a pustule for a week, which he attempted to self-drain and then was treated with oral cephalexin taken for 3 days. On physical examination, he was tachycardic to 125 bpm and febrile to 39.7°C. A 20 cm area of blanching erythema with induration was noted on his back. No fluctuance, bullae or crepitus were evident.

Differential diagnosis

Based on his presenting history, physical examination and initial laboratory findings, the leading diagnosis was cellulitis. There were no gross physical findings of necrotising fasciitis and his Laboratory Risk Indicator for Necrotizing Fasciitis (L-RINEC)⁹ score was not concerning; however, due to his robust inflammatory response, we opted to rule out an underlying collection or, less likely, a necrotising soft tissue infection with cross-sectional imaging.

Investigations

His blood work was only significant for leucocytosis of 16 x 10⁹/L, and he was HIV negative. His calculated L-RINEC score was 1 point (table 1). Given his intense inflammatory response and pain out of proportion to his examination, we decided to perform a CT of the chest to rule out an underlying abscess. Surprisingly, the CT revealed severe fat stranding and subcutaneous gas at the area of concern (figure 1).

Table 1.

L-RINEC score for our patient

L-RINEC		Points
Sodium	137 mEq/L	0
White cell count	16.49 k/µL	1
Haemoglobin	14.8 g/dL	0
Creatinine	1.1 mg/dL	0
C-reactive protein	<150 mg/L	0
Glucose	169 mg/dL	0

L-RNEC, Laboratory Risk Indicator for Necrotising Fasciitis .

Figure 1.

CT scan showing gas in the subcutaneous tissue of the right back (white arows).

Treatment

He was resuscitated with crystalloids and started on intravenous piperacillin/tazobactam, vancomycin and clindamycin. He was emergently taken to the operating room for source control. On opening the skin, necrotic tissue and a large amount of pus were found. The wound was aggressively debrided to a base of viable tissue.

Outcome and follow-up

After the surgery, his inflammatory response improved with normalisation of the white cell count and temperature. He was kept on broad-spectrum antibiotics until his intraoperative wound cultures speciated a pansensitive G. morbillorum on postoperative day 5. He was transitioned to oral clindamycin and discharged home with wound care on postoperative day 7. He followed-up in clinic 2 weeks later; he was doing well and his wound was healing appropriately.

Discussion

According to the Infectious Diseases Society of America, cellulitis is classified as a non-purulent soft tissue infection.¹⁰ It is a common diagnosis, with some studies suggesting it comprise up to 14% of the emergency room visits.¹¹ On the other hand, necrotising soft tissue infections (NSTI) are rare, with an incidence of 0.3–5 per 100 000 habitants.¹² Skin bullae, crepitus and skin necrosis are the classic findings of NSTI. However, these tend to appear late in the course of the disease and are associated with increased morbidity and mortality.¹³ Early signs of NSTI are often indistinguishable from those of cellulitis, which often makes the diagnosis particularly challenging. For this reason, a very high index of suspicion is very important with strong consideration for early surgical exploration, drainage of infected fluid and excisional debridement of necrotic tissue.

The poor sensitivity of early physical examination findings for the diagnosis of NSTI led Wong et al to create the L-RINEC score.⁹ This scoring system uses laboratory data to predict the presence of NSTI with a positive predictive value of 92% for scores above 6. Nevertheless, a recent meta-analysis by Fernando et al showed that the L-RINEC has sensitivity of only 68%, which is lower than originally reported.¹² Our case illustrates the poor sensitivity of physical examination and the L-RINEC score to detect NSTI. This same group concluded that CT has the highest overall sensitivity, which can be as high as 94% with the use of intravenous contrast. Ultrasound is widely available and can be used as an adjunct to aid in the diagnosis; it remains operator dependent with a reported sensitivity of 88%.¹³

Once the diagnosis of NSTI is made, the treatment includes the administration of broad-spectrum antibiotics and emergent surgical intervention to achieve source control. Eighty per cent of the cases are polymicrobial. For those caused by a single organism, Streptococcus spp, methicillin-sensitive and methicillin-resistant Staphylococcus spp, Clostridium spp and Vibrio spp are the most commonly isolated.¹⁴ The offending organism has therapeutic and prognostic implications, as polymicrobial infections tend to have a more benign course.

G. morbillorum is a facultative anaerobe gram-positive coccus considered to be normal flora of the respiratory, urinary and gastrointestinal tracts in humans.² Case reports have implicated G. morbillorum as the causative organism of infections throughout the body, most commonly neurological infections and endocarditis.^2–6 These tend to occur in immunocompromised hosts. There are only three reported cases of G. morbillorum causing necrotising fasciitis. This bacterial species is particularly difficult to isolate in cultures which may partially explain why it is so rarely implicated in NSTI. Certainly, other bacteria may have initiated the original infection and may not have grown out to be identified by our culture.

Of the reported cases where G. morbillorum was inoculated, two patients were intravenous drug users, one was wounded with a fishing hook, and our patient had manipulated a pustule located on his back with a sewing needle contaminated with his own saliva. We hypothesised that opioids created a relative immunocompromised state in these patients,¹⁵ as two of them were actively using opioids and had no other explanation for immunosuppression. All four patients had a good response to antibiotics and surgical debridement, possibly due to a decreased virulence of this commensal bacteria. We agree with other authors that more research is needed to better describe the in vivo and in vitro characteristics of this rare pathogen that may be cultured with future infections in patients without diabetes like the one presented here.

Learning points.

• Necrotising fasciitis is rare compared with cellulitis; however, a high index of suspicion for a necrotising skin and soft tissue infection is needed for a prompt diagnosis as clinical and laboratory findings have low sensitivity.

• Gemella morbillorum is part of the normal human flora. It has the potential to become pathogenic and cause infections such as necrotising fasciitis, especially in immunocompromised or diabetic hosts.

• G. morbillorum is difficult to isolate by culture, it may explain the paucity of similar cases in previously recorded clinical literature. However, further investigations are necessary to study whether the bacteria are developing increased virulence that would lead to novel pathogenesis of necrotising skin and soft tissue infections.