Vitamin D plays an important role in modulating the immune response to infections. Deficiency of vitamin D is a common condition, affecting both the general population and patients in health care facilities. Over the last decade, an increasing body of evidence has shown an association between vitamin D deficiency and an increased risk for acquiring several infectious diseases, as well as poorer outcomes in vitamin D deficient patients with infections. This review details recent developments in understanding the role of vitamin D in immunity, the antibacterial actions of vitamin D, the association between vitamin D deficiency and common infections (like sepsis, pneumonia, influenza, methicillin-resistant Staphylococcus aureus, human immunodeficiency virus type-1 (HIV), and hepatitis C virus (HCV)), potential therapeutic implications for vitamin D replacement, and future research directions.

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Methicillin-resistant Staphylococcus aureus (MRSA), including community-associated and hospital-associated strains, is a major cause of human morbidity and mortality. Treatment options have become limited due to the emergence of MRSA strains with decreased sensitivity to vancomycin, which has long been the first-line therapy for serious infections. This has prompted the search for novel antibiotics that are efficacious against MRSA. Linezolid, an oxazolidinone class of antibiotic, was approved by the Food and Drug Administration in 2000 for treatment of MRSA infections. Since then, there have been a multitude of clinical trials and research studies evaluating the effectiveness of linezolid against serious infections, including pneumonia (both community- and hospital-acquired), skin and soft-tissue infections such as diabetic foot ulcers, endocarditis, osteomyelitis, prosthetic devices, and others. The primary aim of this review is to provide an up-to-date evaluation of the clinical evidence for using linezolid to treat MRSA infections, with a focus on recently published studies, including those on nosocomial pneumonia. Other objectives are to analyze the cost-effectiveness of linezolid compared to other agents, and to review the pharmokinetics and pharmacodynamics of linezolid, emphasizing the most current concepts.