Temporal Cluster Analysis of Deep Sternal Wound Infection in a Regional Quality Collaborative

INTRODUCTION

Deep sternal wound infection (DSWI) is a rare complication associated with high mortality. Seasonal variability in surgical site infections has been demonstrated, however, these patterns have not been applied to DSWI. The purpose of this study was to assess temporal clustering of DSWIs.

METHODS

All cardiac surgery patients who underwent sternotomy were queried from a regional Society of Thoracic Surgeons database from 17 centers from 2001 to 2019. All patients with the diagnosis of DSWI were then identified. Cluster analysis was performed at varying time intervals (monthly, quarterly, and yearly) at the hospital and regional level. DSWI rates were calculated by year and month, and compared using mixed-effects negative binomial regression.

RESULTS

A total of 134,959 patients underwent a sternotomy for cardiac surgery, of whom 469 (0.35%) developed a DSWI. Rates of DSWI per hospital across all years ranged from 0.12% to 0.69%. Collaborative-level rates of DSWIs were the greatest in September (0.44%) and the lowest in January (0.30%). Temporal clustering was not seen across seasonal quarters (high rate in preceeding quarter was not associated with a high rate in the next quarter) (P = 0.39). There were yearly differences across all institutions in the DSWI rates. A downward trend in DSWI rates was seen from 2001 to 2019 (P < 0.001). A difference among hospitals in the cohort was observed (P < 0.001).

CONCLUSIONS

DSWI are a rare event within our region. Unlike other surgical site infection, there does not appear to be a seasonal pattern associated with DSWI.

Spatio-temporal trends of malaria incidence from 2011 to 2017 and environmental predictors of malaria transmission in Myanmar

BACKGROUND

Myanmar bears the heaviest malaria burden in the Greater Mekong Subregion (GMS). This study assessed the spatio-temporal dynamics and environmental predictors of Plasmodium falciparum and Plasmodium vivax malaria in Myanmar.

METHODS

Monthly reports of malaria cases at primary health centers during 2011-2017 were analyzed to describe malaria distribution across Myanmar at the township and state/region levels by spatial autocorrelation (Moran index) and spatio-temporal clustering. Negative binomial generalized additive models identified environmental predictors for falciparum and vivax malaria, respectively.

RESULTS

From 2011 to 2017, there was an apparent reduction in malaria incidence in Myanmar. Malaria incidence peaked in June each year. There were significant spatial autocorrelation and clustering with extreme spatial heterogeneity in malaria cases and test positivity across the nation (P < 0.05). Areas with higher malaria incidence were concentrated along international borders. Primary clusters of P. falciparum persisted in western townships, while clusters of P. vivax shifted geographically over the study period. The primary cluster was detected from January 2011 to December 2013 and covered two states (Sagaing and Kachin). Annual malaria incidence was highest in townships with a mean elevation of 500‒600 m and a high variance in elevation (states with both high and low elevation). There was an apparent linear relationship between the mean normalized difference vegetative index and annual P. falciparum incidence (P < 0.05).

CONCLUSION

The decreasing trends reflect the significant achievement of malaria control efforts in Myanmar. Prioritizing the allocation of resources to high-risk areas identified in this study can achieve effective disease control.

Children's memory "in the wild": examining the temporal organization of free recall from a week-long camp at a local zoo

Free-recall paradigms have greatly influenced our understanding of memory. The majority of this research involves laboratory-based events (e.g., word lists) that are studied and tested within minutes. This literature shows that adults recall events in a temporally organized way, with successive responses often coming from neighboring list positions (i.e., temporal clustering) and with enhanced memorability of items from the end of a list (i.e., recency). Temporal clustering effects are so robust that temporal organization is described as a fundamental memory property. Yet relatively little is known about the development of this temporal structure across childhood, and even less about children's memory search for real-world events occurring over an extended period. In the present work, children (N = 144; 3 age groups: 4-5-year-olds, 6-7-year-olds, 8-10-year-olds) took part in a 5-day summer camp at a local zoo. The camp involved various dynamic events, including daily animal exhibit visits. On day 5, children were asked to recall all the animals they visited. We found that overall recall performance, in terms of number of animals recalled, improved steadily across childhood. Temporal organization and recency effects showed different developmental patterns. Temporal clustering was evident in the response sequences for all age groups and became progressively stronger across childhood. In contrast, the recency advantage, when characterized as a proportion of total responses, was stable across age groups. Thus, recall dynamics in early childhood parallel that seen in adulthood, with continued development of temporal organization across middle to late childhood.

Temporal clustering of neuroblastic tumours in children and young adults from Ontario, Canada

BACKGROUND

The aetiology of neuroblastic tumours is likely to involve both genetic and environmental factors. A number of possible environmental risk factors have been suggested, including infection. If an irregular temporal pattern in incidence is found, this might suggest that a transient agent, such as an infection, is implicated. Previous work has found evidence for temporal clustering in children and young adults living in northern England.

METHODS

We examined data from a second population-based registry from Ontario, Canada to determine whether there was evidence of temporal clustering of neuroblastic tumours. Cases diagnosed in children and young adults aged 0-19 years between 1985 and 2016 were extracted from the population-based Pediatric Oncology Group of Ontario Networked Information System (POGONIS). A modified version of the Potthoff-Whittinghill method was used to test for temporal clustering. Estimates of extra-Poisson variation (EPV) and standard errors (SE) were obtained.

RESULTS

Eight hundred seventy-six cases of neuroblastic tumours were diagnosed during the study period. Overall, no evidence of temporal clustering was found between fortnights, between months or between quarters within years. However, significant EPV was found between years within the full study period (EPV = 1.05, SE = 0.25; P = 0.005).

CONCLUSIONS

The findings are consistent with the possibility that a transient agent, such as an infection that is characterised by 'peaks and troughs' in its occurrence, might be implicated in the aetiology of neuroblastic tumours. However, this pattern may also reflect a long-term increase in the numbers of cases, rather than peaks and troughs.

Universality of stable multi-cluster periodic solutions in a population model of the cell cycle with negative feedback

We study a population model where cells in one part of the cell cycle may affect the progress of cells in another part. If the influence, or feedback, from one part to another is negative, simulations of the model almost always result in multiple temporal clusters formed by groups of cells. We study regions in parameter space where periodic 'k-cyclic' solutions are stable. The regions of stability coincide with sub-triangles on which certain events occur in a fixed order. For boundary sub-triangles with order 'rs1', we prove that the k-cyclic periodic solution is asymptotically stable if the index of the sub-triangle is relatively prime with respect to the number of clusters k and neutrally stable otherwise. For negative linear feedback, we prove that the interior of the parameter set is covered by stable sub-triangles, i.e. a stable k-cyclic solution always exists for some k. We observe numerically that the result also holds for many forms of nonlinear feedback, but may break down in extreme cases.

Neurons in the human medial temporal lobe track multiple temporal contexts during episodic memory processing

Episodic memory requires associating items with temporal context, a process for which the medial temporal lobe (MTL) is critical. This study uses recordings from 27 human subjects who were undergoing surgical intervention for intractable epilepsy. These same data were also utilized in Umbach et al. (2020). We identify 103 memory-sensitive neurons in the hippocampus and entorhinal cortex, whose firing rates predicted successful episodic memory encoding as subjects performed a verbal free recall task. These neurons exhibit important properties. First, as predicted from the temporal context model, they demonstrate reinstatement of firing patterns observed during encoding at the time of retrieval. The magnitude of reinstatement predicted the tendency of subjects to cluster retrieved memory items according to input serial position. Also, we found that spiking activity of these neurons was locked to the phase of hippocampal theta oscillations, but that the mean phase of spiking shifted between memory encoding versus retrieval. This unique observation is consistent with predictions of the “Separate Phases at Encoding And Retrieval (SPEAR)” model. Together, the properties we identify for memory-sensitive neurons characterize direct electrophysiological mechanisms for the representation of contextual information in the human MTL.

Instability of the steady state solution in cell cycle population structure models with feedback

We show that when cell-cell feedback is added to a model of the cell cycle for a large population of cells, then instability of the steady state solution occurs in many cases. We show this in the context of a generic agent-based ODE model. If the feedback is positive, then instability of the steady state solution is proved for all parameter values except for a small set on the boundary of parameter space. For negative feedback we prove instability for half the parameter space. We also show by example that instability in the other half may be proved on a case by case basis.

Recognizing spatial and temporal clustering patterns of dengue outbreaks in Taiwan

BACKGROUND

Dengue fever is the most common arboviral infection in humans, with viral transmissions occurring in more than 100 countries in tropical regions. A global strategy for dengue prevention and control was established more than 10 years ago. However, the factors that drive the transmission of the dengue virus and subsequent viral infection continue unabated. The largest dengue outbreaks in Taiwan since World War II occurred in two recent successive years: 2014 and 2015.

METHODS

We performed a systematic analysis to detect and recognize spatial and temporal clustering patterns of dengue incidence in geographical areas of Taiwan, using the map-based pattern recognition procedure and scan test. Our aim was to recognize geographical heterogeneity patterns of varying dengue incidence intensity and detect hierarchical incidence intensity clusters.

RESULTS

Using the map-based pattern recognition procedure, we identified and delineated two separate hierarchical dengue incidence intensity clusters that comprise multiple mutually adjacent geographical units with high dengue incidence rates. We also found that that dengue incidence tends to peak simultaneously and homogeneously among the neighboring geographic units with high rates in the same cluster.

CONCLUSION

Beyond significance testing, this study is particularly desired by and useful for health authorities who require optimal characteristics of disease incidence patterns on maps and over time. Among the integrated components for effective prevention and control of dengue and dengue hemorrhagic fever are active surveillance and community-based integrated mosquito control, for which this study provides valuable inferences. Effective dengue prevention and control programs in Taiwan are critical, and have the added benefit of controlling the potential emergence of Zika.

Detection and estimation of the increasing trend of cancer incidence in relatively small populations

BACKGROUND

Detection and estimation of trends in cancer incidence rates are commonly achieved by fitting standardized rates to a joinpoint log-linear regression. The efficiency of this approach is inadequate when applied to a relatively low levels of incidence. We compared that approach with the Cuscore test with respect to detecting a log-linear increasing trend of chronic myelomonocytic leukemia (CMML) in datasets simulated to match a province of about 700,000 inhabitants.

METHODS

For better efficiency, we replaced the standardized rate as the dependent variable with a continuous statistic that reflects the inverse of the standardized incidence ratio (SIR). Both procedures were applied to datasets simulated to match published results in the Girona Province of Spain. We also present the use of the q-interval in displaying the temporal pattern of the events. This approach is demonstrated by analyses of CMML diagnoses in Girona County (1994-2008).

RESULTS

The Cuscore was clearly more efficient than regression in detecting the simulated trend. The relative efficiency of the Cuscore is likely to be maintained in even higher levels of incidence. The use of graphical displays in providing clues regarding interpretation of the results is demonstrated.

CONCLUSIONS

The Cuscore test coupled with visual inspection of the temporal pattern of the events seems to be more efficient than regression analysis in detecting and interpreting data suspected to be at elevated risk. A confirmatory analysis is expected to weed out 75% of the superfluous significant results.

Does primary biliary cirrhosis cluster in time?

The aetiology of primary biliary cirrhosis (PBC) is not well established. Previously we found evidence of space-time clustering and seasonal variation in the date of diagnosis, suggesting a possible role for a transient or seasonally varying environmental factor. We examined whether a temporally varying environmental agent may be involved by analysing population-based PBC data from northeast England over 1987-2003. Using an adaptation of a method proposed by Potthoff and Whittinghill, we found significant temporal variation by date of diagnosis at the level of aggregation of one year. However, there was no evidence for general irregular (non-seasonal) temporal clustering within periods less than a year. These results provide little support for the involvement of agents occurring in geographically widespread mini-epidemics, but--taken together with studies of spatial and spatio-temporal clustering--do not preclude the role of more localised sporadic mini-epidemics. Future research should seek to elicit putative environmental agents.