Effect of antibiotics on the bacterial load of meticillin-resistant Staphylococcus aureus colonisation in anterior nares

Summary Prevalence of hospital-acquired meticillin-resistant Staphylococcus aureus (MRSA) infection or colonisation has been associated with antimicrobial consumption. The impact of antibiotic treatment on nasal colonisation is unknown. We conducted a three-month prospective study of 116 patients wi...

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Published in:	The Journal of hospital infection Vol. 70; no. 1; pp. 27 - 34
Main Authors:	Cheng, V.C.C, Li, I.W.S, Wu, A.K.L, Tang, B.S.F, Ng, K.H.L, To, K.K.W, Tse, H, Que, T.L, Ho, P.L, Yuen, K.Y
Format:	Journal Article
Language:	English
Published:	Kent Elsevier Ltd 01-09-2008 Elsevier
Subjects:	Adult Aged Aged, 80 and over Anti-Bacterial Agents - pharmacology Antibacterial agents Antibiotic Prophylaxis Antibiotics Antibiotics. Antiinfectious agents. Antiparasitic agents Bacterial diseases Biological and medical sciences Carrier State - microbiology Cluster Analysis Colony Count, Microbial Cross Infection - microbiology DNA Fingerprinting DNA, Bacterial - genetics Electrophoresis, Gel, Pulsed-Field Environmental Microbiology Female Fluoroquinolones Human bacterial diseases Humans Infectious Disease Infectious diseases Male Medical sciences Methicillin Resistance Meticillin-resistant Staphylococcus aureus Middle Aged Nasal colonisation Nose - microbiology Pharmacology. Drug treatments Prospective Studies Staphylococcal Infections - microbiology Staphylococcal infections, streptococcal infections, pneumococcal infections Staphylococcus aureus Staphylococcus aureus - classification Staphylococcus aureus - drug effects Staphylococcus aureus - isolation & purification Time Factors β-Lactams Fluoroquinolones Nasal colonisation Antibiotics Meticillin-resistant Staphylococcus aureus β-Lactams Nasopharynx Meticillin Penicillin derivatives Infection Antibiotic Fluoroquinolone derivatives Nose Bacteriosis Bacteria Micrococcales Micrococcaceae Antibacterial agent Staphylococcal infection Colonization Public health Staphylococcus aureus
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Summary:	Summary Prevalence of hospital-acquired meticillin-resistant Staphylococcus aureus (MRSA) infection or colonisation has been associated with antimicrobial consumption. The impact of antibiotic treatment on nasal colonisation is unknown. We conducted a three-month prospective study of 116 patients with extranasal MRSA infection or colonisation, whose nasal MRSA bacterial loads were determined during and after various antibiotic courses over a period of three weeks. Environmental swabs were also taken from the near patient environment. Concomitant nasal MRSA carriage was observed in 76.7% of extranasal MRSA-colonised or -infected patients. The median nasal MRSA bacterial load increased significantly from 2.78 (range 0–6.15) to 5.30 (range 2.90–8.41) log10 cfu per swab (cfu/swab) ( P < 0.001) over 21 days during β-lactam therapy. It also increased from 0 (range 0–4.00) to 4.30 (range 0–7.46) log10 cfu/swab ( P = 0.039) over 14 days during fluoroquinolone therapy. Median bacterial loads were significantly higher for β-lactam- and fluoroquinolone-treated patients on day 7 [4.78, range 0–7.30], day 14 [4.30, range 0–7.60] and day 21 [5.30, range 2.90–8.41] than controls not receiving antibiotics ( P < 0.05). These loads then decreased by 2–5 log10 cfu/swab 2 weeks after discontinuation of antibiotics. The environment of patients receiving β-lactam agents (relative risk: 3.55; 95% confidence interval: 1.30–9.62; P = 0.018) or fluoroquinolones (4.32; 1.52–12.31; P = 0.008) demonstrated more MRSA contamination than the environment around control patients (0.79; 0.67–0.93; P = 0.002). Patients on β-lactam or fluoroquinolone therapy have increased incidence of MRSA colonisation and higher nasal bacterial loads, and appear to spread their MRSA into the near patient environment.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0195-6701 1532-2939
DOI:	10.1016/j.jhin.2008.05.019