An evaluation of the usefulness of Staphylococcus aureus serodiagnosis in clinical practice

Serologic Detection of Antibodies Targeting the Leukocidin LukAB Strongly Predicts Staphylococcus aureus in Children With Invasive Infection

BACKGROUND

Staphylococcus aureus is among the most commonly identified causes of invasive bacterial infection in children; however, reliable results from cultures of sterile-site samples often cannot be obtained, which necessitates prescription of a broad empiric antimicrobial agent(s). Children with invasive S aureus infection rapidly generate high antibody titers to the cytotoxin LukAB; therefore, the aim of this study was to assess the diagnostic utility of an anti-LukAB antibody assay for children with musculoskeletal infection (MSKI).

METHODS

We conducted a 2-year prospective study of all eligible children admitted to Vanderbilt Children's Hospital with an MSKI. Acute and convalescent sera were obtained, and antibodies that target LukAB were measured by an enzyme-linked immunosorbent assay.

RESULTS

Forty-two children were enrolled. The median concentrations of LukAB antibodies for children with S aureus infection were 130.3 U/mL in the acute phase and 455 U/mL in the convalescent phase (P < .001). The median concentrations of LukAB antibodies in children with a non-S aureus MSKI were 8.6 U/mL in the acute phase and 9.7 U/mL in the convalescent phase. The assay discriminated between S aureus and non-S aureus infection with areas under the receiver operating characteristic curve of 0.81 (95% confidence interval, 0.67-0.95; P < .001) and 0.95 (95% confidence interval, 0.86-1; P < .001) for samples tested in the acute and follow-up periods, respectively. With no false-negative results, the assay accurately ruled out S aureus in samples obtained during the convalescent phase.

CONCLUSION

Culture-independent diagnostics have the potential to improve care by narrowing antimicrobial therapy on the basis of the likelihood of S aureus infection. The results of this proof-of-concept study suggest that a LukAB serologic assay might be useful in the diagnosis of invasive bacterial infections, and larger-scale validation studies are warranted.

Aetiology and clinical features of facial cellulitis: a prospective study

BACKGROUND

In the early 20th century, the face was the predominant site of cellulitis. Despite a relative decrease in the incidence of facial cellulitis, it is still common. There are few studies on this condition during the last decades. The aim of this study was to describe contemporary aetiological and clinical characteristics of patients admitted to hospital with non-suppurative facial cellulitis.

METHODS

Patients were included prospectively. Clinical details, comorbidities and biochemistry results were recorded. Investigations included cultures of skin swab and blood and tests for streptococcal antibodies during the acute and convalescent stages.

RESULTS

Sixty-five patients were included. Serology, cultures and response to penicillin monotherapy identified probable or confirmed β-haemolytic streptococci (BHS) aetiology in 75% (49/65) of cases. Significant comorbidities were present in 54% (35/65). Fever, chills or rigors before or at admission was noted in 91% (59/65). Patients presented most often with sharply demarcated erythema and raised borders (54/64). Penicillin or penicillinase-resistant penicillin alone or in combination cured 68% (44/65) of the patients. Supplementary clindamycin was used in 28% (18/65), most often only for 1-3 days. Only four patients needed a second course of antibiotics. Clinical failure was more often seen in patients with non-BHS aetiology (p = .037). Few complications were noted; 14.5% (9/62) experienced transient diarrhoea, and only one had confirmed Clostridium difficile infection. No patients developed cerebral venous sinus thrombosis, and there were no fatalities.

CONCLUSIONS

Our findings indicate that BHS are the leading cause of facial cellulitis. Most patients exhibit sharply demarcated lesions and systemic symptoms. Narrow-spectrum β-lactam antibiotics and short hospital stay appear sufficient. Few complications and low recurrence rates were seen.

Multiplex Antibody Detection for Noninvasive Genus-Level Diagnosis of Prosthetic Joint Infection

We developed and evaluated a multiplex antibody detection-based immunoassay for the diagnosis of prosthetic joint infections (PJIs). Sixteen protein antigens from three Staphylococcus species (Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis) (8 antigens), Streptococcus agalactiae (4 antigens), and Propionibacterium acnes (4 antigens) were selected by comparative immunoproteomics using serum samples from PJI cases versus controls. A bead-based multiplex immunoassay that measured serum IgG against purified, recombinant forms of each of the 16 antigens was developed. We conducted a prospective study to evaluate the performance of the assay. A PJI was defined by the presence of a sinus tract and/or positive intraoperative sample cultures (at least one sample yielding a virulent organism or at least two samples yielding the same organism). A total of 455 consecutive patients undergoing revision or resection arthroplasty (hip, 66.3%; knee, 29.7%; shoulder, 4%) at two French reference centers for the management of PJI were included: 176 patients (38.7%) were infected and 279 (61.3%) were not. About 60% of the infections involved at least one of the species targeted by the assay. The sensitivity/specificity values were 72.3%/80.7% for targeted staphylococci, 75%/92.6% for S. agalactiae, and 38.5%/84.8% for P. acnes. The assay was more sensitive for infections occurring >3 months after arthroplasty and for patients with an elevated C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR). However, it detected 64.3% and 58.3% of targeted staphylococcal infections associated with normal CRP and ESR values, respectively. This new multiplex immunoassay approach is a novel noninvasive tool to evaluate patients suspected of having PJIs and provides information complementary to that from inflammatory marker values.

Evidence of streptococcal origin of acute non-necrotising cellulitis: a serological study

Bacteriological diagnosis is rarely achieved in acute cellulitis. Beta-haemolytic streptococci and Staphylococcus aureus are considered the main pathogens. The role of the latter is, however, unclear in cases of non-suppurative cellulitis. We conducted a serological study to investigate the bacterial aetiology of acute non-necrotising cellulitis. Anti-streptolysin O (ASO), anti-deoxyribonuclease B (ADN) and anti-staphylolysin (ASTA) titres were measured from acute and convalescent phase sera of 77 patients hospitalised because of acute bacterial non-necrotising cellulitis and from the serum samples of 89 control subjects matched for age and sex. Antibiotic treatment decisions were also reviewed. Streptococcal serology was positive in 53 (69%) of the 77 cases. Furthermore, ten cases without serological evidence of streptococcal infection were successfully treated with penicillin. Positive ASO and ADN titres were detected in ten (11%) and three (3%) of the 89 controls, respectively, and ASTA was elevated in three patients and 11 controls. Our findings suggest that acute non-necrotising cellulitis without pus formation is mostly of streptococcal origin and that penicillin can be used as the first-line therapy for most patients.