Distinct aetiologies, pathogenesis of two skin, soft-tissue infections
Non-purulent cellulitis and cutaneous abscesses, despite both belonging to the spectrum of skin and soft-tissue infections, are aetiologically different, a new study reports. Further, atypical bacteria may be present in cellulitis patients, indicating novel disease mechanisms.
For the prospective study, a total of 241 US Army soldiers were recruited. Eligible participants were infantry trainees being treated for skin and soft-tissue infections at the Troop Medical Clinic between July 2012 and December 2014.
Upon consent and enrolment into the study, all participants underwent Staphylococcus aureus screening at the following anatomic sites: oropharynx, anterior nares, inguinal and perirectal. Additionally, they accomplished a questionnaire designed to uncover information about previous skin and soft-tissue infections, as well as exposure to relevant risk factors.
Participants who took antibiotics within 2 weeks prior to the study, had animal or human bite wounds, had infection on the face or on surgical sites, showed evidence of sepsis, bacteraemia or deep soft tissue infection, or had any other conditions like diabetes or vascular insufficiency were excluded from the study.
For the purposes of the study, cellulitis was defined as acute infections with diffuse inflammation of the skin and associated structures. At least two of the following symptoms is required: oedema, warmth, erythema, pain or tenderness to palpation. Non-purulent cellulitis, therefore, was defined as cellulitis without exudate, purulent drainage or abscesses.
Abscesses, on the other hand, were defined as acute infections of the skin and associated skin structures. Necessarily, pus accumulation in the dermis or deeper should be present. Other symptoms were tenderness, erythema, and oedema.
Samples of the infections were collected and were then subjected to routine serological and microbiological tests, as well as high-throughput gene sequencing in order to identify the corresponding aetiology.
Of the participants, 201 were included in the analysis of the associated risk factors for skin and soft-tissue infection. From this, it was found that abscesses were correlated with colonization of methicillin-resistant S. aureus (p<0.001), while cellulitis was associated with lower extremity blisters (p=0.01).
On the other hand, the microbiome analysis showed that Rhodanobacter terrae dominated the cellulitis samples, while S. aureus dominated the abscess samples (66.8 and 92.9 percent average abundances, respectively).
The findings imply that, while non-purulent cellulitis and cutaneous abscesses are both categorized as skin and soft-tissue infections, their aetiologies and pathogeneses may be distinct from each other.