Biomedical subjects

M H Craig

Publications and source records attributed to M H Craig.

12 recordsLinked to original sources

PubMed2004

Exploring 30 years of malaria case data in KwaZulu-Natal, South Africa: part I. The impact of climatic factors.

Large parts of Africa are prone to malaria epidemics. Advance epidemic warning would give health services an opportunity to prepare. Because malaria transmission is largely limited by climate, climate-based epidemic warning systems are a real possibility. To develop and test such a system, good long-term malaria and climate data are needed. In KwaZulu-Natal (KZN), South Africa, 30 years of confirmed malaria case data provide a unique opportunity to examine short- and long-term trends. We analysed seasonal case totals and seasonal changes in cases (both log-transformed) against a range of climatic indicators obtained from three weather stations in the highest malaria incidence districts, using linear regression analysis. Seasonal changes in case numbers (delta log cases, dlc) were significantly associated with several climate variables. The two most significant ones were mean maximum daily temperatures from January to October of the preceding season (n=30, r2=0.364, P=0.0004) and total rainfall during the current summer months of November-March (n=30, r2=0.282, P=0.003). These two variables, when entered into the same regression model, together explained 49.7% of the total variation in dlc. We found no evidence of association between case totals and climate. In KZN, where malaria control operations are intense, climate appears to drive the interannual variation of malaria incidence, but not its overall level. The accompanying paper provides evidence that overall levels are associated with non-climatic factors such as drug resistance and possibly HIV prevalence.

Climate↗

PubMed2004

Exploring 30 years of malaria case data in KwaZulu-Natal, South Africa: part II. The impact of non-climatic factors.

Malaria transmission is a multifactorial phenomenon. Climate is a major limiting factor in the spatial and temporal distribution of malaria, but many non-climatic factors may alter or override the effect of climate. Thirty years of monthly malaria incidence data from KwaZulu-Natal province, South Africa, reveal strong medium and long-term trends, which were not present in the climate data. This paper explores various non-climatic factors that may have contributed towards the observed trends. The development of antimalarial drug resistance, available information on human immunodeficiency virus (HIV) prevalence, cross-border people movements, agricultural activities, emergence of insecticide resistance and the case reporting system are reviewed and their potential effect on malaria transmission examined. Single-variable linear regression analysis showed significant association between seasonal case totals (log-transformed) and the measured level of drug resistance (log-transformed) (r2=0.558, n=10, P=0.013) as well as relative measures of HIV infection since 1990 (r2=0.846, n=11, P=0.001). The other factors appear to have affected the level of malaria transmission at certain periods and to some degree. The importance of surveillance and inclusion of non-climatic variables in analysis of malaria data is demonstrated.

Agriculture↗

PubMed2000

Earth observation, geographic information systems and Plasmodium falciparum malaria in sub-Saharan Africa.

This review highlights the progress and current status of remote sensing (RS) and geographical information systems (GIS) as currently applied to the problem of Plasmodium falciparum malaria in sub-Saharan Africa (SSA). The burden of P. falciparum malaria in SSA is first summarized and then contrasted with the paucity of accurate and recent information on the nature and extent of the disease. This provides perspective on both the global importance of the pathogen and the potential for contribution of RS and GIS techniques. The ecology of P. falciparum malaria and its major anopheline vectors in SSA in then outlined, to provide the epidemiological background for considering disease transmission processes and their environmental correlates. Because RS and GIS are recent techniques in epidemiology, all mosquito-borne diseases are considered in this review in order to convey the range of ideas, insights and innovation provided. To conclude, the impact of these initial studies is assessed and suggestions provided on how these advances could be best used for malaria control in an appropriate and sustainable manner, with key areas for future research highlighted.

Africa South of the Sahara↗

PubMed1999

A preliminary continental risk map for malaria mortality among African children.

Approaches to global public health are increasingly driven by an understanding of regional patterns of disease-specific mortality and disability. Current estimates of disease risks associated with Plasmodium falciparum in sub-Saharan Africa remain poorly defined. Through the integration of high-resolution population and climate probability models of P. falciparum transmission, geographical information systems have been used to define the spatial limits of populations exposed to the risk of infection in Africa. These estimates were combined with a range of annual malaria-specific mortality rates, derived from a variety of epidemiological approaches, among children aged 0-4 years. The best estimates of malaria-attributable mortality using this approach ranged between 0. 43 million and 0.68 million deaths per annum among an exposed population of approximately 66 million children in 1990. Despite the limitations of modelled transmission and population distributions, these empirical approaches to probabilities of infection risk and epidemiological data on mortality provide a novel approach to present and projected burdens of malaria mortality, as discussed here by Bob Snow, Marlies Craig, Uwe Deichmann and Dave le Sueur.

Africa South of the Sahara↗

PubMed1999

A climate-based distribution model of malaria transmission in sub-Saharan Africa.

Malaria remains the single largest threat to child survival in sub-Saharan Africa and warrants long-term investment for control. Previous malaria distribution maps have been vague and arbitrary. Marlies Craig, Bob Snow and David le Sueur here describe a simple numerical approach to defining distribution of malaria transmission, based upon biological constraints of climate on parasite and vector development. The model compared well with contemporary field data and historical 'expert opinion' maps, excepting small-scale ecological anomalies. The model provides a numerical basis for further refinement and prediction of the impact of climate change on transmission. Together with population, morbidity and mortality data, the model provides a fundamental tool for strategic control of malaria.

Africa South of the Sahara↗

PubMed1998

Mapping malaria transmission intensity using geographical information systems (GIS): an example from Kenya.

That there are so few examples of the use of epidemiological maps in malaria control may be explained by the lack of suitable, spatially defined data and of an understanding of how epidemiological variables relate to disease outcome. However, recent evidence suggests that the clinical outcomes of infection are determined by the intensity of parasite exposure, and developments in geographical information systems (GIS) provide new ways to represent epidemiological data spatially. In the present study, parasitological data from 682 cross-sectional surveys conducted in Kenya were abstracted and spatially defined. Risks of infection with Plasmodium falciparum among Kenyan children, estimated from combinations of parasitological, geographical, demographic and climatic data in a GIS platform, appear to be low for 2.9 million, stable but low for another 1.3 million, moderate for 3.0 million and high for 0.8 million. (Estimates were not available for 1.4 million children.) Whilst the parasitological data were obtained from a variety of sources across different age-groups and times, these markers of endemicity remained relatively stable within the broad definitions of high, moderate and low transmission intensity. Models relating ecological and climatic features to malaria intensity and improvements in our understanding of the relationships between parasite exposure and disease outcome will hopefully provide a more rational basis for malaria control in the near future.

Climate↗

PubMed1995

Pancreatic injuries from blunt trauma.

Pancreatic injuries from blunt trauma are infrequent, and their diagnosis and management can be extremely difficult. Over the past 10 years we treated 13 patients with major pancreatic injuries from blunt trauma. Twelve had been involved in motor vehicle collisions, none of whom were wearing seat belts. One patient was injured in an assault. Only five patients had physical findings suggesting intra-abdominal injury. Serum amylase levels were elevated in seven of the nine patients (78%) in whom this test was obtained. Computed tomography scans demonstrated pancreatic injury in three of the four patients in whom it was performed. The five patients in whom peritoneal lavage was performed had free intraperitoneal blood from injuries to other abdominal viscera. One injury was diagnosed by ultrasound. Injuries were equally distributed throughout the pancreas, with two injuries in the head, three in the body, five in the tail, and three with injuries in both the head and the body. Five patients had ductal injuries. All patients underwent celiotomy. Eight patients required no operative management of their pancreatic injuries other than drainage. Injury Severity Score averaged 28.5 +/- 2.6 (mean +/- standard error), and mean hospital stay was 31 +/- 9.8 days. One patient with delayed diagnosis of a pancreatic injury developed a pseudocyst, but all other complications and prolonged hospitalizations were due to injuries to the head, chest, other abdominal organs, or extremities. All patients survived. The diagnosis of blunt pancreatic injury requires a high index of suspicion, and diagnostic studies may demonstrate only subtle signs of injury. Most injuries can be managed by localized resection and/or drainage.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Injuries↗

PubMed1995

Postsurgical gout.

Although catabolic events are known to precipitate gout, postsurgical gout has rarely been reported. We identified the charts of 302 patients treated over a 10-year period in a university center who carried the diagnosis of gout and who also had a surgical procedure. Fifty-two patients (42 male, 10 female) were found to have had a postsurgical episode of gouty arthritis. Ages ranged from 20 to 82 years (mean 60.1 +/- 2.1). Forty-five patients had a history of gout, 22 of whom were receiving medication and 23 who were not receiving chronic therapy. In seven patients the postsurgical event was their first attack. Attacks occurred 1-17 days (mean 4.2 +/- 0.5 [SE]) after surgical admission. Most attacks were in the lower extremity, but classic podagra was uncommon. Essentially all patients were febrile (100.7 +/- 0.2 degrees F) compared with admission (99.0 +/- 0.1 degree) (P < 0.001). There was a trend toward leukocytosis in the group as a whole, but the relationship of leukocytosis to the gout attack was most clearly seen in patients admitted for noninflammatory conditions (9.4 +/- 0.7 versus 12.8 +/- 0.8 x 1000 WBC/mm3, P < 0.001). Uric acid levels were elevated but did not follow the course of the attack. Most patients underwent a variety of tests and consultative evaluations because of their undiagnosed febrile episode. Once the diagnosis was established, all patients responded quickly to nonsteroidal anti-inflammatory drugs or colchicine. Despite evidence of a significant inflammatory response, no patient proved to have a suppurative focus as the source of their febrile episode.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1995

Major gastroenteric injuries from blunt trauma.

Hollow visceral injuries are far less common in blunt abdominal trauma than in penetrating abdominal trauma. From 1982 through 1993 we treated 50 patients with 57 major blunt injuries to the gut, defined as perforation, transection, or devascularization. Thirty-two patients (64%) were injured in motor vehicle collisions. Of these, 29 wore no restraints; three were wearing lap belts (none wore lap-shoulder restraints). Mean injury Severity Score (ISS) in patients wearing lap belts was 13.3, compared with 28.6 in the 29 patients who were not using restraint devices (P < 0.01). Small bowel perforations were the most frequent injuries, followed by devascularization of the small bowel, colorectal injuries, duodenal, and gastric perforations. ISS and mortality rates were lowest in small bowel injuries and higher in the less common colonic and gastroduodenal injuries. Except for those patients with perforations of the small bowel, most patients had associated injuries to the head, chest, or abdominal solid organs that were largely responsible for morbidity and mortality. Injuries to the abdominal hollow viscera are unusual following blunt trauma, but are the result of very high energy truncal trauma, and are associated with multiple additional injuries. Most alert patients had physical findings suggestive of peritoneal irritation, but when diagnostic testing was necessary, peritoneal lavage was superior to computed tomography scanning (false negatives = 6.7% versus 36%, respectively; P < 0.05). A high index of suspicion is necessary to avoid diagnostic delays that can lead to severe complications and death.

Accidents, Traffic↗

PubMedDate not supplied

Field and laboratory comparative evaluation of ten rapid malaria diagnostic tests.

The paper reports on a comparative evaluation of 10 rapid malaria tests available in South Africa in 1998: AccuCheck (AC, developmental), Cape Biotech (CB), ICT Malaria Pf (ICT1) and Pf/Pv (ICT2), Kat Medical (KAT), MakroMal (MM), OptiMAL (OP), ParaSight-F (PS), Quorum (Q), Determine-Malaria (DM). In a laboratory study, designed to test absolute detection limits, Plasmodium falciparum-infected blood was diluted with uninfected blood to known parasite concentrations ranging from 500 to 0.1 parasites per microlitre (P/microL). The 50% detection limits were: ICT1, 3.28; ICT2, 4.86; KAT, 6.36; MM, 9.37; CB, 11.42; DM, 12.40; Q, 16.98; PS, 20; AC, 31.15 and OP, 91.16 P/microL. A field study was carried out to test post-treatment specificity. Blood samples from malaria patients were tested with all products (except AC and DM) on the day of treatment and 3 and 7 days thereafter, against a gold standard of microscopy and polymerase chain reaction (PCR). OP and PS produced fewer false-positive results on day 7 (18 and 19%, respectively) than the other rapid tests (38-56%). However, microscopy, PCR, OP and PS disagreed largely as to which individuals remained positive. The tests were further compared with regard to general specificity, particularly cross-reactivity with rheumatoid factor, speed, simplicity, their ability to detect other species, storage requirements and general presentation.

Animals↗

PubMedDate not supplied

Comparative evaluation of four techniques for the diagnosis of Plasmodium falciparum infections.

Four diagnostic techniques for Plasmodium falciparum infection were evaluated against serial parasite dilutions and on identical field samples. These were (i) Giemsa-stained thick blood films (GTF), (ii) acridine orange-stained thick (AOTF) and thin (AOTnF) blood films, (iii) the quantitative buffy coat technique (QBC); and (iv) the ParaSight-F dipstick test (PS). PS had a consistently higher sensitivity and speed, was easiest to learn, and required no laboratory facility. The 100% sensitivity cut-off points against known parasite densities (per mm3) were: PS, 30; GTF, 84; QBC, 84; AOTnF, 84; AOTF, 149. In the field study, test sensitivities compared with examination of 800 microscope fields of a Giemsa-stained thin blood film were PS, 96.6%; AOTF, 93.1%; GTF, 91.4%; QBC, 89.7%; AOTnF, 82.8%. In the dilution study, one false positive result was recorded with QBC; in the field study there was one false positive each with PS, AOTnF and AOTF. When a newly trained microscopist examined samples of the parasite dilutions, the 100% sensitivity cut-off points were AOTF, 84; GTF, 140; QBC, 390. Total handling time was shortest with PS regardless of whether samples were processed individually or in batches of 10 or 100. The ParaSight-F test is recommended as the diagnostic tool for the future.

Enzyme-Linked Immunosorbent Assay↗

PubMedDate not supplied

Models to predict the intensity of Plasmodium falciparum transmission: applications to the burden of disease in Kenya.

There is an increasing need to provide spatial distribution maps of the clinical burden of Plasmodium falciparum malaria in Africa. Recent evidence suggests that risk groups and the clinical spectrum of severe malaria are related to the intensity of P. falciparum transmission. Climate operates to affect the vectorial capacity of P. falciparum transmission and this is particularly important in the Horn of Africa and parts of East Africa. We have used a fuzzy logic climate suitability model to define areas of Kenya unsuitable for stable transmission. Kenya's unstable transmission areas can be divided into areas where transmission potential is limited by low rainfall or low temperature and, combined, encompass over 8 million people. Among areas of stable transmission we have used empirical data on P. falciparum infection rates among 124 childhood populations in Kenya to develop a climate-based statistical model of transmission intensity. This model correctly identified 75% (95% confidence interval CI 70-85) of 3 endemicity classes (low, < 20%; high, > or = 70%; and intermediate parasite prevalences). The model was applied to meteorological and remote sensed data using a geographical information system to provide estimates of endemicity for all of the 1080 populated fourth level administrative regions in Kenya. National census data for 1989 on the childhood populations within each administrative region were projected to provide 1997 estimates. Endemicity-specific estimates of morbidity and mortality were derived from published and unpublished sources and applied to their corresponding exposed-to-risk childhood populations. This combined transmission, population and disease-risk model suggested that every day in Kenya approximately 72 and 400 children below the age of 5 years either die or develop clinical malaria warranting in-patient care, respectively. Despite several limitations, such an approach goes beyond 'best guesses' to provide informed estimates of the geographical burden of malaria and its fatal consequences in Kenya.

Child, Preschool↗