Stochastic Spatial Models in Ecology: A Statistical Physics Approach

Ecosystems display a complex spatial organization. Ecologists have long tried to characterize them by looking at how different measures of biodiversity change across spatial scales. Ecological neutral theory has provided simple predictions accounting for general empirical patterns in communities of competing species. However, while neutral theory in well-mixed ecosystems is mathematically well understood, spatial models still present several open problems, limiting the quantitative understanding of spatial biodiversity. In this review, we discuss the state of the art in spatial neutral theory. We emphasize the connection between spatial ecological models and the physics of non-equilibrium phase transitions and how concepts developed in statistical physics translate in population dynamics, and vice versa. We focus on non-trivial scaling laws arising at the critical dimension of spatial neutral models, and their relevance for biological populations inhabiting two-dimensional environments. We conclude by discussing models incorporating non-neutral effects in the form of spatial and temporal disorder, and analyze how their predictions deviate from those of purely neutral theories.MAM is grateful to the Spanish-MINECO for financial support (under Grant FIS2013-43201-P; FEDER funds

Phase II, Randomized, Multicenter, Double-Blind, Placebo-Controlled Trial of a Polyclonal Anti-Staphylococcus aureus Capsular Polysaccharide Immune Globulin in Treatment of Staphylococcus aureus Bacteremia▿

New treatment modalities are needed for the treatment of infections due to multidrug-resistant Staphylococcus aureus. S. aureus capsular polysaccharide immune globulin (Altastaph) is a polyclonal immune globulin preparation that is being developed as adjunctive therapy for persons with S. aureus infections complicated by bacteremia. In a phase II, multicenter, randomized, double-blind, placebo-controlled trial, 40 subjects with documented S. aureus bacteremia received standard therapy plus either Altastaph at 200 mg/kg of body weight in each of two infusions 24 h apart or placebo. During the 42-day observation period, antibody pharmacokinetics and safety were the primary characteristics studied. Information regarding the resolution of bacteremia and fever was also analyzed. Anti-type-5 and anti-type-8 capsular antibody levels peaked after the second infusion at 550 μg/ml and 419 μg/ml, respectively, and remained above 100 μg/ml at day 28. A total of 316 adverse events were noted in 39 of 40 subjects. Infusion-related adverse events in Altastaph recipients were infrequent and similar to those among recipients of commercial intravenously administered immunoglobulin G products. Five of 21 (23%) subjects in the Altastaph group died, whereas 2 of 18 (11%) subjects in the placebo group died (P = 0.42). Compared to the control patients, the Altastaph recipients had a shorter median time to the resolution of fever (2 days and 7 days, respectively; P = 0.09) and a shorter length of hospital stay (9 days and 14 days, respectively; P = 0.03). However, these findings are exploratory, and there were few differences in the other variables measured. High levels of opsonizing antibodies were maintained for the initial 4 weeks. Although the study was not powered to show efficacy, these preliminary findings and safety profile suggest that Altastaph may be an effective adjunct to antibiotics and warrants further investigation (ClinicalTrials.gov number NCT00063089)

Elimination of Staphylococcus aureus Nasal Carriage in Health Care Workers: Analysis of Six Clinical Trials with Calcium Mupirocin Ointment

Six double-blind, independently randomized studies evaluated the efficacy and safety of calcium mupirocin ointment in eliminating nasal carriage of Staphylococcus aureus among health care workers. Healthy volunteers with stable nasal carriage of S. aureus (n = 339) received either calcium mupirocin ointment (n = 170) or an identical placebo ointment (n = 169) intranasally for 5 days. Nasal carriage was eliminated 48–96 hours after completion of treatment in 130 (91%) of 143 evaluable volunteers receiving mupirocin but in only 8 (6%) of 142 evaluable volunteers receiving placebo. The 85% crude difference represents a 90% pooled (adjusted) estimate of the risk difference (95% confidence interval, 0.86–0.95) and a risk ratio of 16 (P \u3c.0001). This effect of treatment with mupirocin was observed consistently (risk ratio, 8–32) in all six centers. In addition, 96 of the 130 mupirocin-treated volunteers and 1 of the 8 placebo-treated volunteers who were culture-negative at the end of therapy remained free of S. aureus 4 weeks after treatment. Adverse events in each treatment arm were mild and equally frequent. These data, consistent across six institutions, demonstrate that calcium mupirocin ointment administered intranasally for 5 days is safe and effective in eliminating stable nasal carriage of S. aureus