Frotis superficial frente a aspiración percutánea para el diagnóstico de infección de herida crónica: ¿resultados discrepantes?

Abstract

We report a prospective, observational study on 112 patients with chronic wound of different aetiologies and with clinical diagnosis of suspected infection. The microbiological results obtained were compared by means of taking two kinds of sample: surface swab and fine needle aspiration. The average number of micro-organisms isolated by sample was 2.1 for surface swab vs. 1.8 for aspiration. The percentage total effective concordance (TEC) for the microbiological diagnosis for the two methods studied was 62.5%. The TEC obtained for the two majority chronic wound groups was 80% (P=0.219) for pressure sores and 54% (P<0.001) for venous ulcers. Concordance between the two methods for Staphylococcus aureus was 69.4%, 73.3% for gram negative bacilli and 88.9% for anaerobic micro-organisms. In our work, the aspirate produced significant false negatives for pathogens of major clinical relevance for skin and soft tissue infection such as Streptococcus pyogenes. We cannot state that the swab mainly reflects colonisation but rather that, if the sample is based on suspected infection and processed by means of a semi-quantitative count, the isolates may actually reflect infection.