Chris Skelly

Leptospirosis in American Samoa - Estimating and Mapping Risk Using Environmental Data

Background The recent emergence of leptospirosis has been linked to many environmental drivers of disease transmission. Accurate epidemiological data are lacking because of under-diagnosis, poor laboratory capacity, and inadequate surveillance. Predictive risk maps have been produced for many diseases to identify high-risk areas for infection and guide allocation of public health resources, and are particularly useful where disease surveillance is poor. To date, no predictive risk maps have been produced for leptospirosis. The objectives of this study were to estimate leptospirosis seroprevalence at geographic locations based on environmental factors, produce a predictive disease risk map for American Samoa, and assess the accuracy of the maps in predicting infection risk. Methodology and Principal Findings Data on seroprevalence and risk factors were obtained from a recent study of leptospirosis in American Samoa. Data on environmental variables were obtained from local sources, and included rainfall, altitude, vegetation, soil type, and location of backyard piggeries. Multivariable logistic regression was performed to investigate associations between seropositivity and risk factors. Using the multivariable models, seroprevalence at geographic locations was predicted based on environmental variables. Goodness of fit of models was measured using area under the curve of the receiver operating characteristic, and the percentage of cases correctly classified as seropositive. Environmental predictors of seroprevalence included living below median altitude of a village, in agricultural areas, on clay soil, and higher density of piggeries above the house. Models had acceptable goodness of fit, and correctly classified ∼84% of cases. Conclusions and Significance Environmental variables could be used to identify high-risk areas for leptospirosis. Environmental monitoring could potentially be a valuable strategy for leptospirosis control, and allow us to move from disease surveillance to environmental health hazard surveillance as a more cost-effective tool for directing public health interventions.

The regionality of campylobacteriosis seasonality in New Zealand

New Zealand has one of the highest incidences of campylobacteriosis in the developed world, which leads a global trend of increasing notifications of Campylobacter infections over the last decade. Foodborne and waterborne transmission have been implicated as significant mechanisms in the complex ecology of the disease in New Zealand. We examined both regional and temporal variation in notification rates to gain some insight into the role of the New Zealand environments in modifying disease incidence. Firstly, there is a marked difference in the seasonality of campylobacteriosis between the North and South Islands of New Zealand. The Far North and much of the rural North Island were found to display relatively low summer incidence and small inter-seasonal variation. Secondly, there appears to be a dispersed grouping of North Island urban areas, including Auckland, Hamilton, Napier and their hinterlands as well as a few areas on the South Island that exhibit higher summer incidence and more seasonality than the first group. Thirdly, Christchurch, Dunedin, much of the South Island and the lower North Island cities of Wellington and Upper Hutt appear to experience the highest summer incidence and strongest inter-seasonal variation in New Zealand. These three broad groupings of campylobacteriosis seasonality, constructed using a principal components analysis, suggest that the importance of transmission routes may vary regionally in New Zealand. The observed variation in seasonal incidence indicates a complex ecology that is unlikely to be explained by a single dominant transmission route across these three groupings.

Modeling vadose zone liquid water fluxes: Infiltration, runoff, drainage, interflow

Because of the large water storage capacity of soil relative to the atmosphere, changes in soil moisture storage can significantly affect the regional atmospheric budgets of water and energy on monthly, seasonal and longer time scales. Therefore proper modeling of soil liquid water processes is essential to a correct representation of the climate system. This study focuses on the class of summary models of liquid water fluxes in the vadose, or unsaturated zone of the soil, which are applicable to global or regional climate modeling studies. Fourteen such models are represented in this intercomparison study. Observational data from the HAPEX experiment provide validation. Because only limited observational data were available to constrain these models during their development and validation, the models have evolved very diverse treatments of the relevant processes: the basic Darcian (soil internal) and Hortonian (surface liquid flow) processes, as well as the boundary conditions of baseflow drainage and lateral interflow. The annual total local runoff is systematically underestimated by all but one of the participant models. This is one of the few significant biases between the consensus of participant models and the observations. The modeled runoff, averaged over the 14 models, differs from the budget estimate from observations by about 40%. During the period of runoff generation (late winter and early spring) the average model fails to deplete the soil water store as rapidly as is observed, a result consistent with the underprediction of runoff. One cannot rule out insufficient characterization of the field site soils as a primary cause of these discrepancies. Results suggest that model sources of the discrepancy are about equally likely to be related to the prediction of bare soil evaporation (discussed elsewhere in this issue) as they are to the parameterization of runoff and drainage processes.

Social deprivation and the public health risks of community drinking water supplies in New Zealand

Study objective: Quantitative evidence linking environmental exposures and social status at sub-national scales is surprisingly limited. This study investigated the public health risks associated with community water supplies in relation to social status in New Zealand. Design: An ecological study using a Geographic Information System (GIS) to compare the grade of community water supplies with an index of social deprivation for small areas. Setting: New Zealand. Participants: The New Zealand population usually resident in meshblocks (census areas) with a community water supply (70% of the 1996 population of 3.6 million people). Main results: People living in deprived areas are exposed to greater public health risks from community water supplies. In urban areas, the odds of water supplies being high risk were 3.76 times greater for the most deprived decile compared with the least deprived decile (95% CI: 2.95 to 4.78). Conclusions: It is probable that deprived communities in New Zealand are experiencing a disproportionate burden of adverse health effects as a result of poor water quality.

Emergence of new leptospiral serovars in American Samoa - ascertainment or ecological change?

BackgroundLeptospirosis has recently been discussed as an emerging infectious disease in many contexts, including changes in environmental drivers of disease transmission and the emergence of serovars. In this paper, we report the epidemiology of leptospiral serovars from our study of human leptospirosis in American Samoa in 2010, present evidence of recent serovar emergence, and discuss the potential epidemiological and ecological implications of our findings.MethodsSerovar epidemiology from our leptospirosis seroprevalence study in 2010 was compared to findings from a study in 2004. The variation in geographic distribution of the three most common serovars was explored by mapping sero-positive participants to their place of residence using geographic information systems. The relationship between serovar distribution and ecological zones was examined using geo-referenced data on vegetation type and population distribution.ResultsHuman leptospirosis seroprevalence in American Samoa was 15.5% in 2010, with serological evidence that infection was caused by three predominant serovars (Hebdomadis, LT 751, and LT 1163). These serovars differed from those identified in an earlier study in 2004, and were not previously known to occur in American Samoa. In 2010, serovars also differed in geographic distribution, with variations in seroprevalence between islands and different ecological zones within the main island.ConclusionsOur findings might indicate artefactual emergence (where serovars were long established but previously undetected), but we believe the evidence is more in favour of true emergence (a result of ecological change). Possibilities include changes in interactions between humans and the environment; introduction of serovars through transport of animals; evolution in distribution and/or abundance of animal reservoirs; and environmental changes that favour transmission of particular serovars.Future research should explore the impact of ecological change on leptospirosis transmission dynamics and serovar emergence, and investigate how such new knowledge might better target environmental monitoring for disease control at a public health level.

RATES OF NOTIFIED CRYPTOSPORIDIOSIS AND QUALITY OF DRINKING WATER SUPPLIES IN AOTEAROA, NEW ZEALAND

An ecological study was conducted in New Zealand to examine the relationship between incidence of human cryptosporidiosis and indicators of community drinking-water supply quality, using routinely collected data from June 1996 to August 1998. A total of 790 cases of cryptosporidiosis lived in communities with a registered drinking-water supply. Within each category of the grading system there was a wide range of rates of cryptosporidiosis. The lowest mean rates of notified cryptosporidiosis were observed in communities served by drinking water supplies with completely satisfactory public health gradings, and the highest rates in communities served by ungraded drinking- water supplies. Mean rates of notified cryptosporidiosis in drinking-water zones that complied with New Zealand drinking-water standards were lower than rates in zones that did not comply with the standards. Current methods of assessing the quality of New Zealand drinking-water supplies reflect in broad terms the risk to human health from Cryptosporidium parvum. Data limitations and uncontrolled confounding mean that the excess risk due to poor quality of the drinking water supply cannot be quantified, but improvements in drinking water quality are likely to be associated with health benefits at the population level. Occurrence of a high proportion of cases in drinking water supplies with a satisfactory public health grading highlights the importance of non-waterborne modes of transmission in human cryptosporidiosis. 7 2000 Elsevier Science Ltd. All rights reserved

Sunshine, rainfall, humidity and child pneumonia in the tropics: time-series analyses.

Few studies have formally examined the relationship between meteorological factors and the incidence of child pneumonia in the tropics, despite the fact that most child pneumonia deaths occur there. We examined the association between four meteorological exposures (rainy days, sunshine, relative humidity, temperature) and the incidence of clinical pneumonia in young children in the Philippines using three time-series methods: correlation of seasonal patterns, distributed lag regression, and case-crossover. Lack of sunshine was most strongly associated with pneumonia in both lagged regression [overall relative risk over the following 60 days for a 1-h increase in sunshine per day was 0·67 (95% confidence interval (CI) 0·51-0·87)] and case-crossover analysis [odds ratio for a 1-h increase in mean daily sunshine 8-14 days earlier was 0·95 (95% CI 0·91-1·00)]. This association is well known in temperate settings but has not been noted previously in the tropics. Further research to assess causality is needed.

Field epidemiology of an outbreak of dengue fever in Charters Towers, Queensland: are insect screens protective?

Abstract: Between March and July 1993 a dengue virus epidemic swept through Charters Towers, a rural North Queensland mining community of 10 000. This clearly delineated outbreak provided an ideal opportunity to carry out one of the few field epidemiological studies of dengue in Australia. The epicurve was consistent with that of a point source outbreak, 18 weeks in duration and peaking at four weeks. A basic reproduction number for the dengue epidemic of 1.99 indicates a similar rate of spread to that found in dengue epidemics overseas. A female‐to‐male sex ratio of 1.7:1 was obtained for the 238 cases identified. An age‐and sex‐matched retrospective case—control study showed that cases were significantly more likely to live in unscreened houses than were controls (McNemar X2=56, 1 df, P<0.0001). Despite being generally accepted, an association between insect screens and a reduced incidence of mosquito‐borne diseases has not previously been demonstrated in Australia. We speculate that unscreened housing facilitates the initial spread of a dengue epidemic.

Water, water quality and health

This chapter identifies the role environmental tracking plays in identifying public health water hazard and water quality issues. It outlines public health issues to be examined and provides an integrated overview of water and diseases by combining knowledge of the hydrologic cycle, which describes how water serves as a significant component of exposure pathways, with the tenants of public health surveillance.