Asthma Outbreaks Research Articles

The Impact of Air Pollution on the Incidence of Asthma: A Comparative Analysis of Regional Factors

Air quality is closely related to human health and has attracted the attention of governments and people around the world. This paper aims to study whether there is a concrete link between the development of asthma and air pollution. By adopting comparative analysis, it examines three regions (Seoul, Sydney, and San Joaquin Valley) in terms of how different sources of air pollution affect the incidence of asthma. The results indicate that agricultural and industrial pollution cause asthma outbreaks worst in certain areas. The implication of this paper is that the local governments should develop programs to train public health professionals through public health networks. These health networks provide practical training in epidemiology and strategic planning, and help achieve effectively Communication with other health professionals and the public through public speaking, academic reports and scientific investigations, while advocating for other community managers for improved community health. In the meanwhile, it is crucial to improve local air quality through reasonable environmental regulation.

Prediction of airborne pollen and sub-pollen particles for thunderstorm asthma outbreaks assessment

When exposed to convective thunderstorm conditions, pollen grains can rupture and release large numbers of allergenic sub-pollen particles (SPPs). These sub-pollen particles easily enter deep into human lungs, causing an asthmatic response named thunderstorm asthma (TA). Up to now, efforts to numerically predict the airborne SPP process and to forecast the occurrence of TAs are unsatisfactory. To overcome this problem, we have developed a physically-based pollen model (DREAM-POLL) with parameterized formation of airborne SPPs caused by convective atmospheric conditions. We ran the model over the Southern Australian grass fields for 2010 and 2016 pollen seasons when four largest decadal TA epidemics happened in Melbourne. One of these TA events (in November 2016) was the worldwide most extreme one which resulted to nine deaths and hundreds of hospital patient presentations. By executing the model on a day-by-day basis in a hindcast real-time mode we predicted SPP peaks exclusively only when the four major TA outbreaks happened, thus achieving a high forecasting success rate. The proposed modelling system can be easily implemented for other geographical domains and for different pollen types.

Thunderstorm allergy and asthma: state of the art.

Thunderstorm-triggered asthma (TA) can be defined as the occurrence of acute asthma attacks immediately following a thunderstorm during pollen seasons. Outbreaks have occurred across the world during pollen season with the capacity to rapidly inundate a health care service, resulting in potentially catastrophic outcomes for allergic patients. TA occurs when specific meteorological and aerobiological factors combine to affect predisposed atopic patients with IgE-mediated sentitization to pollen allergens. Thunderstorm outflows can concentrate aeroallergens, most commonly grass pollen but also other pollens such as Parietaria and moulds in TA, at ground level to release respirable allergenic particles after rupture by osmotic shock related to humidity and rainfall. Inhalation of high concentrations of these aeroallergens by sensitized individuals can induce early asthmatic responses which can be followed by a late inflammatory phase. There is evidence that, during pollen season, thunderstorms can induce allergic asthma outbreaks, sometimes also severe asthma crisis and sometimes deaths in patients suffering from pollen allergy. It has been observed that changes in the weather such as rain or humidity may induce hydratation of pollen grains during pollen seasons and sometimes also their fragmentation which generates atmospheric biological aerosols carrying allergens. Asthma attacks are induced for the high concentration at ground level of pollen grains which may release allergenic particles of respirable size after rupture by osmotic shock. In other words, it is a global health problem observed in several cities and areas of the world that can strike without sufficient warning, inducing sometimes severe clinical consequences also with deaths of asthma patients. Due to constant climate change, future TA events are likely to become more common, more disastrous and more unpredictable, as a consequence it is important to have deep knowledge on this topic to prevent asthma attacks. Other environmental factors, such as rapid changes in temperature and agricultural practices, also contribute to causing TA.

Allergenicity at component level of sub-pollen particles from different sources obtained by osmolar shock: A molecular approach to thunderstorm-related asthma outbreaks.

The so-called "thunderstorm asthma" (TA) is an uncommon but dramatic outbreak of asthma attacks occurring during a thunderstorm in the pollen and moulds season. Mechanisms which make the pollen able to enter the deeper airways and provoke severe asthma symptoms are still unclear. To test the hypothesis that sub-pollen particles (SPPs) originated from the rupture by an osmotic shock of pollen associated with TA contain allergens. After hydration, SPPs released from pollen grains of grass, pellitory, olive, cypress, ragweed and birch were isolated and determined by microscopy. Allergens were determined by in vitro ELISA inhibition tests indirectly using the sera from 10 polyreactive patients. An inhibition <50% was considered as negative, 50%-75% moderate and>75% complete. The inhibition experiments showed that the SPPs from birch and cypress were unable to inhibit serum IgE reactivity to Bet v 1 and Cup a 1, respectively. Ragweed SPPs inhibited ragweed pollen extract and Amb a 1 by 75.8±0.11% and 81.2±0.15%, respectively. Olive and pellitory SPPs retained almost the whole IgE-binding capability in all cases tested. Grass SPPs inhibited 32±0.06% of Lolium perenne Lol p 1 and 65% of Phleum pratense extracts, but results were highly variable for individual allergens (97.5%-0.03% for Phl p 2, 45.3±0.12% for Phl p 5, 24.7±0.22% for Phl p 6, and 38.3±0.2% for Phl p 1). Inhibition experiments confirm the hypothesis that SSPs obtained after the osmotic shock of pollen involved in TA, namely grass, pellitory and olive tree pollen, contain allergens and therefore they can induce severe asthma attacks during thunderstorms.

A Probable Mechanism for Recurring Outbreak of Respiratory Syndrome During Autumn Season in Ahvaz City, Iran

Background: Recurring annual asthma or asthma-like outbreak in Ahvaz City, Iran, has become a serious public health problem. A toxic gas, a chemical compound, or an allergen with unknown nature and mechanism leads to severe asthma outbreaks each year. Bronchospasm, cough, dyspnea, chest tightness, and wheezing are the main symptoms of these attacks. Oxygen and anti-asthma therapy are effective treatments in outbreak management. Based on our findings, it is hypothesized that vast amounts of ammonium nitrate used in agriculture underlay high concentrations of nitrate. This substance is transported by PM10 and is the main cause of the respiratory outbreak. Methods: The concentration of nitrate was determined by the ion chromatography method in dust samples during 2015-2016. Using spectroscopic methods, the effect of nitrate ions on hemoglobin oxidation and methemoglobin formation was studied. Results: Our results indicate that the concentration of ammonium nitrate in dust collected from indoor spaces is five times higher than the levels allowed amount in airborne pollutants. Our findings also indicate that this concentration of nitrate in the bloodstream can instantly increase methemoglobin percent to 18% with symptomatic consequences. Conclusion: The exact mechanism proposed by this study is that inhaled nitrate or nitric acid finally increases the nitrate in the circulation of affected individuals. Hemoglobin oxidation and methemoglobin formation are the subsequent events leading to methemoglobinemia with asthma-like reactions seen in Ahvaz respiratory syndrome. Restricting or even prohibiting ammonium nitrate application in agriculture seems to be an urgent measure to stop Ahvaz's recurring respiratory syndrome.

Harnessing Tweets for Early Detection of an Acute Disease Event.

Melbourne, Australia, witnessed a thunderstorm asthma outbreak on 21 November 2016, resulting in over 8,000 hospital admissions by 6 P.M. This is a typical acute disease event. Because the time to respond is short for acute disease events, an algorithm based on time between events has shown promise. Shorter the time between consecutive incidents of the disease, more likely the outbreak. Social media posts such as tweets can be used as input to the monitoring algorithm. However, due to the large volume of tweets, a large number of alerts may be produced. We refer to this problem as alert swamping. We present a four-step architecture for the early detection of the acute disease event, using social media posts (tweets) on Twitter. To curb alert swamping, the first three steps of the algorithm ensure the relevance of the tweets. The fourth step is a monitoring algorithm based on time between events. We experiment with a dataset of tweets posted in Melbourne from 2014 to 2016, focusing on the thunderstorm asthma outbreak in Melbourne in November 2016. Out of our 18 experiment combinations, three detected the thunderstorm asthma outbreak up to 9 hours before the time mentioned in the official report, and five were able to detect it before the first news report. With appropriate checks against alert swamping in place and the use of a monitoring algorithm based on time between events, tweets can provide early alerts for an acute disease event such as thunderstorm asthma.

Epidemiological estimates of Acute Respiratory diseases and Asthma using Geostatistical tools in Rawalpindi, Pakistan

Event Abstract Back to Event Epidemiological estimates of Acute Respiratory diseases and Asthma using Geostatistical tools in Rawalpindi, Pakistan Ahmad S. Saeed1* and Javiria Younis1 1 Fatima Jinnah Women University, Pakistan Respiratory diseases are a major cause of death in developing countries. Allocation of scarce resources in developing countries is a major problem for which identification of high risk areas and patterns of disease spread are necessary. A Cohort study design was used in this study.Using 2011-2015 diseased person data for Acute Respiratory Diseases and Asthma from District Health Office, Rawalpindi we examined emerging hotspots and spatiotemporal trends of diseases spread by using geostatistical tools in ArcGIS 10.2. Climatic parameters and land use was also correlated with disease incidence to examine the effect on disease spread. Pattern of diseases was found to be random throughout the district and incidence rate per thousand people was highest for tehsil Kotli Sattian. Most of the hotspots lied in the areas with large settlements and dense vegetation cover. Cold related Asthma and Acute Respiratory Diseases was also revealed along with the seasonal outbreaks of Asthma in mid spring and autumn. Shift of Asthma towards denser vegetation areas and towards agricultural areas was seen for Acute Respiratory Diseases. Climatic parameters such as temperature and rainfall also showed strong correlation with disease incidence. Rawalpindi district is prone to cold weather related Asthma and Acute Respiratory Diseases. There is a need to conduct detailed study on aeroallergens and air pollution in study area especially in high risk areas to control the spread and intensity of these respiratory diseases. Acknowledgements Authors are thankful to District Health Office for provision of data Keywords: Respiratory diseases, Hotspot analysis, Air Pollutants, Pakistan, Asthama Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019. Presentation Type: Regular oral presentation Topic: Emerging GIS, data science and sensor technologies adapted to animal, plant and human health, including precision medicine and precision farming Citation: Saeed AS and Younis J (2019). Epidemiological estimates of Acute Respiratory diseases and Asthma using Geostatistical tools in Rawalpindi, Pakistan. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00005 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Jun 2019; Published Online: 27 Sep 2019. * Correspondence: Mx. Ahmad S Saeed, Fatima Jinnah Women University, Rawalpindi, Pakistan, drsaeed@fjwu.edu.pk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ahmad S Saeed Javiria Younis Google Ahmad S Saeed Javiria Younis Google Scholar Ahmad S Saeed Javiria Younis PubMed Ahmad S Saeed Javiria Younis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Thunderstorm asthma outbreak, a rare phenomenon in southwest Iran: patients' perspectives.

Previous studies that described thunderstorm asthma, which is a rare event, are not being well explained. This study was conducted, to describe the patient perspective on their asthma attack experience during Ahvaz post-rain phenomenon. We have interviewed patients present in the Naft clinic of Ahvaz, during 28th October and the first week of November 2015. Recruitment was continued as saturation ensued by 33 participants. An inductive content analysis was used to evaluate the interviews. The key finding indicated a climatic condition, direct or indirect contact with rain, history of allergy, and physical conditions are the main categories. The patient emphasized the importance of dust, humidity, first autumn rainfall, and environmental air pollution in occurrences of the event. When exposed to further rains (third rainfall onward), they were less likely to experience dyspnea or shortness of breath. However, being indoor or out at the time of rainfall reported not to be related to the onset of asthma exacerbation. This study yielded that patients' asthma outbreak is a climate-related health impact and many individual factors triggering this issue. Patients concerns need future investigation and public health emergency planning and response arrangements.

Thunderstorm asthma: a special kind of asthma epidemics

Thunderstorm asthma is an asthma outbreaks related to thunderstorm. This paper reviews the related literature in database and reports on the internet, and summarizes the concept, mechanism, patient characteristics and hazards of thunderstorm asthma, providing some suggestions for the prevention and education of the patients with asthma, so as to provide health reference for asthma prevention and education. Key words: Review; Asthma; Health education; Allergy; Thunderstorm

Thunderstorm asthma outbreak of November 2016: a natural disaster requiring planning.

Thunderstorm asthma outbreak of November 2016: a natural disaster requiring planning.

Effects of diesel exhaust particle exposure on a murine model of asthma due to soybean.

BackgroundExposure to soybean allergens has been linked to asthma outbreaks. Exposure to diesel exhaust particles (DEP) has been associated with an increase in the risk of asthma and asthma exacerbation; however, in both cases the underlying mechanisms remain poorly understood, as does the possible interaction between the two entities.ObjectiveTo investigate how the combination of soybean allergens and DEP can affect the induction or exacerbation of asthma in a murine model.MethodsBALB/c mice received intranasal instillations of saline, 3 or 5 mg protein/ml soybean hull extract (SHE), or a combination of one of these three solutions with DEP. Airway hyperresponsiveness (AHR), pulmonary inflammation in bronchoalveolar lavage, total serum immunoglobulin E and histological studies were assessed.ResultsA 5 mg protein/ml SHE solution was able by itself to enhance AHR (p = 0.0033), increase eosinophilic inflammation (p = 0.0003), increase levels of IL-4, IL-5, IL-13, IL-17A, IL-17F and CCL20, and reduce levels of IFN-γ. The combination of 5 mg protein/ml SHE with DEP also produced an increase in AHR and eosinophilic inflammation, but presented a slightly different cytokine profile with higher levels of Th17-related cytokines. However, while the 3 mg protein/ml SHE solution did not induce asthma, co-exposure with DEP resulted in a markedly enhanced AHR (p = 0.002) and eosinophilic inflammation (p = 0.004), with increased levels of IL-5, IL-17F and CCL20 and decreased levels of IFN-γ.Conclusions & clinical relevanceThe combination of soybean allergens and DEP is capable of triggering an asthmatic response through a Th17-related mechanism when the soybean allergen concentration is too low to promote a response by itself. DEP monitoring may be a useful addition to allergen monitoring in order to prevent new asthma outbreaks.

Assessment of thunderstorm-induced asthma using Google Trends

An asthma outbreak of hospitalizations and deaths was noticed in Australia (November 2016) and in Kuwait (December 2016). This outbreak was clearly demonstrated using Google Trends (GT), a Web-based surveillance tool of interest in clinical practice.

The Role of Mesoscale-Convective Processes in Explaining the 21 November 2016 Epidemic Thunderstorm Asthma Event in Melbourne, Australia

AbstractA major thunderstorm asthma epidemic struck Melbourne and surrounding Victoria, Australia, on 21 November 2016, which led to multiple deaths, a flood of residents seeking medical attention for respiratory problems, and an overwhelmed emergency management system. This case day had all the classic ingredients for an epidemic, including high rye grass pollen concentrations, a strong multicellular thunderstorm system moving across the region, and a large population of several million people in the vicinity of Melbourne. A particular characteristic of this event was the strong, gusty winds that likely spread the pollen grains and/or allergenic contents widely across the region to increase population exposure. This exploratory case study is the first to examine the usefulness of low-to-middle-atmospheric thermodynamic information for anticipating epidemic thunderstorm asthma outbreaks by allowing the forecast of strong downdraft winds. The authors investigated the utility of several mesoscale products derived from atmospheric soundings such as downdraft convective available potential energy (DCAPE) and indices for predicting surface wind gusts such as microburst wind speed potential index (MWPI) and a wind gust index (GUSTEX). These results indicate that DCAPE levels reached “high” to “very high” thresholds for strong downdraft winds in the lead-up to the thunderstorm, and the MWPI and GUSTEX indices accurately predicted the high maximum surface wind observations. This information may be useful for diagnostic and prognostic assessment of epidemic thunderstorm asthma and in providing an early warning to health practitioners, emergency management officials, and residents in affected areas.

Thunderstorm and asthma outbreaks during pollen season

An increasing body of evidence shows the occurrence of asthma epidemics, sometimes also severe, during thunderstorms in the pollen season in various geographical zones. The main hypothesis explaining association between thunderstorms and asthma claims that thunderstorms can concentrate pollen grains at ground level; these grains may then release allergenic particles of respirable size in the atmosphere after their rupture by osmotic shock. During the first 20-30 minutes of a thunderstorm, patients suffering from pollen allergy may inhale a high concentration of the allergenic material dispersed into the atmosphere, which can, in turn, induce asthmatic reactions, often severe. Subjects without asthma symptoms but affected by seasonal rhinitis can also experience an asthma attack. All subjects affected by pollen allergy should be alerted to the danger of being outdoors during a thunderstorm in the pollen season, as such events may be an important cause of severe bronchial obstruction. Considering this background, it is useful to predict thunderstorms during pollen season and, thus, to prevent thunderstorm-related clinical event. However, it is also important to focus on therapy, and it is not sufficient that subjects at risk of asthma follow a correct therapy with bronchodilators, but they also need to inhale corticosteroids, using both in case of emergency.

The relationship between body mass index and increased airway reactivity based on methacholine challenge test results.

IntroductionAccording to the reports of the United States National Bureau of Statistics regarding the prevalence of obesity among adults and children and also asthma outbreak, the relationship between asthma and obesity in developed countries is taken into consideration.AimRelationship between body mass index and increased airway reactivity based on methacholine challenge test results.Material and methodsIt was a retrospective cross-sectional study done on 256 patients who were referred to the lung clinic of the Imam Khomeini Hospital of Ahvaz with symptoms of hypersensitivity of the airways. The patients, who had normal spirometry, were examined by the methacholine challenge test and then they were divided in two groups with positive and negative test results.ResultsThe patients of this study were 12–84 years old and their average age was 36.3 ±12.1 years. Their mean body mass index (BMI) was 28 ±4.7 kg/m2 in the group with positive methacholine and 26.7 ±4.9 kg/m2 in the group with negative methacholine (p = 0.04). It was shown that there has been a statistically significant relationship between BMI and positive methacholine challenge test results (apart from confounding effects of other variables). It seems that the positivity rate of methacholine test rises by 1.06 with an increase in BMI by each unit (p < 0.05).ConclusionsAccording to the results of this study, it can be said that in high BMI there is a statistically significant association between gender (female) and a positive methacholine challenge test result; but there is no statistically significant association between the methacholine dose and BMI.

Madeira—a tourist destination for asthma sufferers

Madeira Island is a famous tourist destination due to its natural and climatic values. Taking into account optimal weather conditions, flora richness and access to various substrates facilitating fungal growth, we hypothesised a very high risk of elevated fungal spore and pollen grain concentrations in the air of Funchal, the capital of Madeira. Concentration levels of the most allergenic taxa were measured from 2003 to 2009, using a 7-day volumetric air sampler, followed by microscopy analysis. Dependence of bioaerosols on the weather conditions and land use were assessed using spatial and statistical tools. Obtained results were re-visited by a comparison with hospital admission data recorded at the Dr. Nélio Mendonça Hospital in Funchal. Our results showed that despite propitious climatic conditions, overall pollen grain and fungal spore concentrations in the air were very low and did not exceed any clinically established threshold values. Pollen and spore peak concentrations also did not match with asthma outbreaks in the winter. Identification of places that are "free" from biological air pollution over the summer, such as Madeira Island, is very important from the allergic point of view.

An overview of thunderstorm-associated asthma outbreak in southwest of Iran.

The aim of this study was to report the characteristics and treatment strategies of all patients with acute bronchospasm who were presented to the emergency departments of Ahvaz, Iran, following the occurrence of a thunderstorm on November 2, 2013. A total of 2000 patients presenting with asthma attacks triggered by thunderstorm were interviewed and an initial questionnaire was completed for each individual. After twenty days, patients were asked to complete a supplementary questionnaire, but only 800 of them accepted to do so. The majority of subjects was aged 20–40 years (60.5%) and had no history of asthma in most cases (60.0%). The symptoms had started outdoors for 60.0% of the participants. In most patients, the onset of the condition was on November 2. Short-acting β 2-agonist (salbutamol) and aminophylline were the most commonly prescribed medications in the emergency department. Upon the second interview, 85.3% of the patients were still symptomatic. Overall, 63.6% did not have a follow-up visit after hospital discharge, although all of them were referred to the specialist. The findings of the present study suggest that thunderstorm-associated asthma could affect young adults with no gender priority, with or without asthma history, which put a strain on emergency medical services.

A trans-disciplinary overview of case reports of thunderstorm-related asthma outbreaks and relapse

There is evidence that, during the pollen season, thunderstorms can be associated with allergic asthma outbreaks in patients suffering from pollen allergy [1], and there are observations in favour of the possibility that thunderstorms disturb ground-level pollen grains, which may release allergenic particles of respirable size into the atmosphere after rupture by osmotic shock [2, 3]. During the first 20–30 min of a thunderstorm, patients suffering from pollen allergy may inhale a high concentration of the allergenic material that is dispersed into the atmosphere, which in turn can induce (severe) asthmatic reactions in some cases [3–6]. Even though thunderstorms can induce severe asthma attacks or exacerbations, they are neither frequent nor responsible for a high amount of disease exacerbation. However, physicians and pollen allergy patients should know the mechanisms involved in the release of allergens from airborne pollen grains during thunderstorms and the associated risk in view of prevention. Information about the risk of an asthma attack is also relevant in subjects affected only by seasonal allergic rhinitis who can inhale lower airways pollen aerosol. In addition, there is a potential risk of thunderstorm-related relapse of asthma attacks in some patients. This constitutes a major concern nowadays as the possibility of thunderstorm-associated asthma outbreaks have become of dramatic actuality due to the “highly likely” increase in frequency of heavy precipitation events, including thunderstorms, projected by the climate change scenarios for the future decades [7]. The purpose of this article is to gather existing trans-disciplinary data on thunderstorm-related asthma attacks and potential relapse in the same patient. Pollen grain, which is a causative agent of allergic respiratory responses, is among the commonest allergens and pollen allergy due to its elevated prevalence and associated costs is now a public health problem …

Systematic review of respiratory case definitions in metalworking fluid outbreaks

Since the mid-1990s, outbreaks of asthma and extrinsic allergic alveolitis (EAA) have been identified in workers exposed to metalworking fluids (MWFs). The cause of these outbreaks remains to be determined. To identify and review all previously published occupational lung disease case definitions and diagnostic criteria that have been utilized during MWF outbreak investigations. Respiratory outbreaks due to MWFs were identified by a systematic literature search for articles published between 1990 and October 2011. Investigations reporting the usage of disease case definitions or diagnostic criteria for respiratory disease were reviewed and summarized. The literature search identified 35 papers relating to 27 outbreaks of respiratory disease in MWF-exposed workers. Fourteen case definitions for MWF-related respiratory disease were identified: seven for EAA, five for occupational asthma and one each for humidifier fever and industrial bronchitis. A single paper was identified where any comparison of different disease case definitions (for EAA) had been performed. A range of case definitions and diagnostic criteria for MWF respiratory disease have been utilized in outbreak investigations, but the majority have been produced for individual outbreak investigations without previous validation. It may be difficult to compare the findings of future workplace studies without a more standardized approach to case identification and diagnosis.

Systematic Review of Respiratory Outbreaks Associated with Exposure to Water-Based Metalworking Fluids

Potential demographic risk factors for outbreaks of respiratory disease due to water-based metalworking fluids (MWFs) were investigated through systematic review of published outbreak investigations. Search terms were selected by a multidisciplinary team, assisted by an experienced library information service. Several computerized literature databases were searched for articles published between January 1990 and October 2011, relating to ill health outbreaks due to MWFs. Papers meeting the search criteria were reviewed in detail, and their references checked for additional articles. Study design and demographic details of the outbreak were extracted from the selected articles and entered into standardized evidence tables. Thirty-five articles relating to investigations of 27 outbreaks of respiratory ill health attributed to MWF exposure were identified. The majority of reports were case series of disease or observational cross-sectional studies of symptoms and hygiene measurements. Eight of the outbreak investigations included an element of case-control analysis. Most outbreaks were from the USA, had occurred in large car- or aeronautical-manufacturing plants, and were associated with the use of central shared sumps. Hygiene studies have not demonstrated consistent risk factors for respiratory outbreaks, in terms of the type of MWF utilized, degree of microbial contamination, or levels of personal exposure. Six studies were identified that found workers with MWF exposure during outbreaks were more likely to report respiratory or systemic symptoms than unexposed control workers. Six case-control analyses were also identified that found workers with extrinsic allergic alveolitis (EAA) were more likely to demonstrate certain immune responses to microbial contaminants and/or used MWFs than workers without EAA. Despite a number of detailed workplace and immunological studies of asthma and alveolitis outbreaks in MWF-exposed workforces, our understanding of their aetiology remains limited.