Using simulated infectious disease outbreaks to inform site selection and sample size for individually randomized vaccine trials during an ongoing epidemic.

BACKGROUND: Novel strategies are needed to make vaccine efficacy trials more robust given uncertain epidemiology of infectious disease outbreaks, such as arboviruses like Zika. Spatially resolved mathematical and statistical models can help investigators identify sites at highest risk of future transmission and prioritize these for inclusion in trials. Models can also characterize uncertainty in whether transmission will occur at a site, and how nearby or connected sites may have correlated outcomes. A structure is needed for how trials can use models to address key design questions, including how to prioritize sites, the optimal number of sites, and how to allocate participants across sites. METHODS: We illustrate the added value of models using the motivating example of Zika vaccine trial planning during the 2015-2017 Zika epidemic. We used a stochastic, spatially resolved, transmission model (the Global Epidemic and Mobility model) to simulate epidemics and site-level incidence at 100 high-risk sites in the Americas. We considered several strategies for prioritizing sites (average site-level incidence of infection across epidemics, median incidence, probability of exceeding 1% incidence), selecting the number of sites, and allocating sample size across sites (equal enrollment, proportional to average incidence, proportional to rank). To evaluate each design, we stochastically simulated trials in each hypothetical epidemic by drawing observed cases from site-level incidence data. RESULTS: When constraining overall trial size, the optimal number of sites represents a balance between prioritizing highest-risk sites and having enough sites to reduce the chance of observing too few endpoints. The optimal number of sites remained roughly constant regardless of the targeted number of events, although it is necessary to increase the sample size to achieve the desired power. Though different ranking strategies returned different site orders, they performed similarly with respect to trial power. Instead of enrolling participants equally from each site, investigators can allocate participants proportional to projected incidence, though this did not provide an advantage in our example because the top sites had similar risk profiles. Sites from the same geographic region may have similar outcomes, so optimal combinations of sites may be geographically dispersed, even when these are not the highest ranked sites. CONCLUSION: Mathematical and statistical models may assist in designing successful vaccination trials by capturing uncertainty and correlation in future transmission. Although many factors affect site selection, such as logistical feasibility, models can help investigators optimize site selection and the number and size of participating sites. Although our study focused on trial design for an emerging arbovirus, a similar approach can be made for any infectious disease with the appropriate model for the particular disease.

Host-phage interactions and modeling for therapy.

Phage are drivers of numerous ecological processes on the planet and have the potential to be developed into a therapy alternative to antibiotics. Phage at all points of their life cycle, from initiation of infection to their release, interact with their host in some manner. More importantly, to harness their antimicrobial potential it is vital to understand how phage interact with the eukaryotic environment in the context of applying phage for therapy. In this chapter, the various mechanisms of phage interplay with their hosts as part of their natural life cycle are discussed in depth for Gram-positive and negative bacteria. Further, the literature surrounding the various models utilized to develop phage as a therapeutic are examined, and how these models may improve our understanding of phage-host interactions and current progress in utilizing phage for therapy in the clinical environment.

Antibacterial activity of vB_AbaM_PhT2 phage hydrophobic amino acid fusion endolysin, combined with colistin against Acinetobacter baumannii.

Phage lytic enzymes are promising antimicrobial agents. In this study, an endolysin derived from vB_AbaM_PhT2 (vPhT2), was identified. This endolysin represented the conserved lysozyme domain. Recombinant endolysin (lysAB- vT2) and hydrophobic fusion endolysin (lysAB-vT2-fusion) were expressed and purified. Both endolysins showed lytic activity against bacterial crude cell wall of Gram-negative bacteria. The MIC of lysAB-vT2-fusion was 2 mg/ml corresponding to 100 µM, while the MIC of lysAB-vT2 was more than 10 mg/ml (400 µM). Combination of lysAB-vT2-fusion with colistin, polymyxin B or copper was synergistic against A. baumannii (FICI value as 0.25). Antibacterial activity of lysAB-vT2-fusion plus colistin at the fractional inhibitory concentrations (FICs) revealed that it can inhibit Escherichia coli, Klebsiella pneumoniae and various strains of extremely drug-resistant A. baumannii (XDRAB) and phage resistant A. baumannii. The lysAB- vT2-fusion still retained its antibacterial activity after incubating the enzyme at 4, 20, 40 and 60 °C for 30 min. The lysAB-vT2-fusion could inhibit the mature biofilm, and incubation of lysAB-vT2-fusion with T24 human cells infected with A. baumannii led to a partial reduction of LDH release from T24 cells. In summary, our study highlights the antimicrobial ability of engineered lysAB-vT2-fusion endolysin, which can be applied for the control of A. baumannii infection.

Severity of Acute Graft-versus-Host Disease and Associated Healthcare Resource Utilization, Cost, and Outcomes.

Acute graft-versus-host disease (aGVHD) contributes to poor outcomes and increased healthcare resource utilization (HRU) after allogeneic hematopoietic stem cell transplantation (HCT). However, HRU and the economic burden of aGVHD based on severity of the disease is not well characterized. Our study cohort comprised 290 adults who underwent allogeneic HCT between 2010 and 2018. Costs, HRU, and all-cause mortality in the 100-day and 365-day periods after HCT were compared between patients with aGVHD and those without aGVHD. The impact of aGVHD severity and gastrointestinal (GI) involvement on mortality, HRU, and economic burden was also evaluated. Medical costs and total hospital length of stay (LOS) were retrieved from administrative data that allocate costs to services based on departmental input for resource use and were adjusted to 2018 dollars. The Wilcoxon rank-sum test was used to compare the number of inpatient days and total costs. Multivariable linear regression was fitted on log-transformed costs. Compared with patients without aGVHD, those with aGVHD had a significantly greater median hospital LOS (28 days versus 22 days) and higher rates of intensive care unit (ICU) admission (13% versus 6%) and rehospitalization (59% versus 38%) during the first 100 days post-HCT. The presence of grade I-II aGVHD significantly prolonged the hospital LOS by a median of 3 days and increased the readmission rate by 18%, whereas grade III-IV aGVHD was associated with a nearly 30% increase in the readmission rate and a doubling of inpatient LOS, ICU admission rate, and mortality in the first 100 days post-HCT. Compared with the absence of aGVHD, lower GI involvement in aGVHD was also associated with increased risk of readmission (30%) and twice as many inpatient days, doubling the likelihood of ICU admission and mortality over the first 100 days. Similar findings were observed over days 101 to 365 post-HCT. The mean cost attributable to aGVHD regardless of grade was $60,923 in the first 100 days post-HCT. This cost varied by grade. The mean aGVHD- attributable costs were $18,071 for grade I, $36,115 for grade II and $120,929 for grade III/IV aGVHD and $114,668 for aGVHD involving the lower GI tract. In the 101- to 365-day period, the mean attributable aGVHD cost regardless of grade was $17,527. This cost also varied by grade. There were no additional aGVHD-attributable costs for grade I, but the mean aGVHD-attributable costs were $9743 for grade II, $62,220 for grade III/IV, and $55,724 for aGVHD with lower GI involvement compared with the controls without aGVHD. High-grade aGVHD and GI involvement in aGVHD, especially lower GI aGVHD, is associated with a considerably increased mortality and healthcare economic burden. Therefore, it is imperative that new therapeutic strategies be developed for this patient population.