A Qualitative Exploration of Social Contact Patterns Relevant to Airborne Infectious Diseases in Northwest Bangladesh

In South Asia, the burden of infectious diseases is high. Socioeconomically and culturally-defined social interaction patterns are considered to be an important determinant in the spread of diseases that are transmitted through person-to-person contact. Understanding of the contact patterns in this region can be helpful to develop more effective control measures. Focus group discussions were used in exploring social contact patterns in northwest Bangladesh. The patterns were assessed for perceived relevance to the spread of airborne infectious diseases, with special focus on diseases, like leprosy and tuberculosis, in which the role of social determinants is well-recognized. Highly-relevant social contact patterns inside the home and the neighbourhood, across age and sex groups, were reported in all group discussions. Outside the home, women and girls reported relevant contacts limited to the close neighbourhood while men mentioned high relevant contacts beyond. This implies that, in theory, infectious diseases can easily be transmitted across age and sex groups in and around the home. Adult men might play a role in the transmission of airborne infectious diseases from outside this confined area since only this group reported highly-relevant social contacts beyond the home. This concept needs further exploration but control programmes in the South Asian region could benefit from considering differences in social contact patterns by gender for risk assessments and planning of preventive interventions.Key words: Airborne infectious diseases, Leprosy, Social contact patterns, Tuberculosis, Bangladesh     

Mitigation strategies to reduce the generation and transmission of airborne highly pathogenic avian influenza virus particles during processing of infected poultry

Airborne transmission of H5N1 highly pathogenic avian influenza (HPAI) viruses has occurred among poultry and from poultry to humans during home or live-poultry market slaughter of infected poultry, and such transmission has been experimentally reproduced. In this study, we investigated simple, practical changes in the processing of H5N1 virus-infected chickens to reduce infectious airborne particles and their transmission. Our findings suggest that containing the birds during the killing and bleeding first step by using a disposable plastic bag, a commonly available cooking pot widely used in Egypt (halla), or a bucket significantly reduces generation of infectious airborne particles and transmission to ferrets. Similarly, lack of infectious airborne particles was observed when processing vaccinated chickens that had been challenged with HPAI virus. Moreover, the use of a mechanical defeatherer significantly increased total number of particles in the air compared to manual defeathering. This study confirms that simple changes in poultry processing can efficiently mitigate generation of infectious airborne particles and their transmission to humans.     

Using data on social contacts to estimate age-specific transmission parameters for respiratory-spread infectious agents

The estimation of transmission parameters has been problematic for diseases that rely predominantly on transmission of pathogens from person to person through small infectious droplets. Age-specific transmission parameters determine how such respiratory agents will spread among different age groups in a human population. Estimating the values of these parameters is essential in planning an effective response to potentially devastating pandemics of smallpox or influenza and in designing control strategies for diseases such as measles or mumps. In this study, the authors estimated age-specific transmission parameters by augmenting infectious disease data with auxiliary data on self-reported numbers of conversational partners per person. They show that models that use transmission parameters based on these self-reported social contacts are better able to capture the observed patterns of infection of endemically circulating mumps, as well as observed patterns of spread of pandemic influenza. The estimated age-specific transmission parameters suggested that school-aged children and young adults will experience the highest incidence of infection and will contribute most to further spread of infections during the initial phase of an emerging respiratory-spread epidemic in a completely susceptible population. These findings have important implications for controlling future outbreaks of novel respiratory-spread infectious agents.     

Modelling the transmission of airborne infections in enclosed spaces

The Wells-Riley equation for modelling airborne infection in indoor environments is incorporated into an SEIR epidemic model with a short incubation period to simulate the transmission dynamics of airborne infectious diseases in ventilated rooms. The model enables the effect of environmental factors such as the ventilation rate and the room occupancy to be examined, and allows the long-term impact of infection control measures to be assessed. A theoretical parametric study is carried out to demonstrate how changes to both the physical environment and infection control procedures may potentially limit the spread of short-incubation-period airborne infections in indoor environments such as hospitals.     

医疗机构中微生物气溶胶的特性与作用

医疗机构中传染性病原体的传播方式包括,接触传播、飞沫传播和空气传播。大量研究表明,2019新型冠状病毒病(COVID-19)以飞沫传播和接触传播为主。近日,国家卫生健康委员会相继发布《新型冠状病毒肺炎诊疗方案》的第六版和第七版,有关传播途径分别新增"在相对封闭的环境中长期暴露于高浓度气溶胶情况下存在经气溶胶传播的可能。"以及"由于在粪便及尿中可分离到新型冠状病毒,应注意粪便及尿对环境污染造成气溶胶或接触传播"。为此,本文就医疗机构传染性病原体传播途径,空气传播的3种分类方法,特别是气溶胶的定义、产生、生存、传播、作用以及控制等方面进行文献综述。     

Prolonged outbreak of giardiasis with two modes of transmission

Large outbreaks of giardiasis caused by person-to-person transmission, or a combination of transmission routes, have not previously been reported. A large, prolonged giardiasis outbreak affected families belonging to a country club in a suburb of Boston, Massachusetts, during June-December 2003. We conducted a retrospective cohort study to determine the source of this outbreak. Giardiasis-compatible illness was experienced by 149 (25%) respondents to a questionnaire, and was laboratory confirmed in 97 (65%) of these cases. Of the 30 primary cases, exposure to the children's pool at the country club was significantly associated with illness (risk ratio 3.3, 95% confidence interval 1.7-6.5). In addition, 105 secondary cases probably resulted from person-to-person spread; 14 cases did not report an onset date. This outbreak illustrates the potential for Giardia to spread through multiple modes of transmission, with a common-source outbreak caused by exposure to a contaminated water source resulting in subsequent prolonged propagation through person-to-person transmission in the community. This capacity for a common-source outbreak to continue propagation through secondary person-to-person spread has been reported with Shigella and Cryptosporidium and may also be a feature of other enteric pathogens having low infectious doses.     

Targeted social distancing design for pandemic influenza

Targeted social distancing to mitigate pandemic influenza can be designed through simulation of influenza's spread within local community social contact networks. We demonstrate this design for a stylized community representative of a small town in the United States. The critical importance of children and teenagers in transmission of influenza is first identified and targeted. For influenza as infectious as 1957-58 Asian flu (=50% infected), closing schools and keeping children and teenagers at home reduced the attack rate by >90%. For more infectious strains, or transmission that is less focused on the young, adults and the work environment must also be targeted. Tailored to specific communities across the world, such design would yield local defenses against a highly virulent strain in the absence of vaccine and antiviral drugs.     

Considerations on isolation rooms and alternative pressure ventilation systems

The health-care facility environment is involved in disease transmission in essentially two different situations: 1. in cases where patients are immunocompromised and require protection from infections; 2. in cases of inadvertent exposure to environmental or airborne pathogens that can aggravate patients' existent disease and cause illness among health-care personnel. Environmental infection-control strategies and engineering controls can effectively prevent transmission of these infections. In particular the ventilation system is fundamental to the control of the concentration of airborne contaminants within a hospital isolation room because it establishes and maintains appropriate pressure differentials within special care areas of the building. Thus the incidence of health-care-associated infections can be minimized by adherence to ventilation standards suggested in the guidelines for specialized care environments such as Airborne Infection Isolation rooms (AII, as in situation 2 above), and Protective Environments (PE) rooms (as in situation 1 above). This report is a comparative review of the principal guidelines and strategies existing in the international scientific literature for the prevention of environment-associated infections in healthcare facilities using pressure differentials (positive pressure for PE rooms, negative pressure for AII rooms). The purpose of the review is also to investigate the state-of-the-art use of the "alternative pressure rooms", i.e., areas furnished with a ventilation system capable of switching pressure from positive to negative according to patients' needs. The results of the present analysis indicate an unenthusiastic reaction to these "alternative pressure rooms", although there is no scientific evidence against their use.     

The Northumberland epidemic of foot-and-mouth disease, 1966.

The spread of foot-and-mouth disease during an epidemic in Northumberland in July, August and September 1966 was analysed. Although strong emitters, for example pigs, were not involved, in 18 of the 32 outbreaks spread could be attributed to the airborne route and in another 4, spread by this route was the most likely. Airborne spread was in general between 1 and 8 km but on two occasions as much as 20 km. Other means of spread included movement by animals, people and vehicles and carriage of virus between animals in neighbouring fields. No spread by milk or milk lorries took place. Sheep were involved in 9 farms; on each, lesions older than 48 h were found and it is likely that the sheep were the source of virus for other animals, especially cattle, on the farm and on neighbouring farms. The analysis suggests that control measures such as slaughtering direct contacts, as used in this epidemic, or ring vaccination as well as movement control would be effective in limiting spread.     

Bias due to secondary transmission in estimation of attributable risk from intervention trials

BACKGROUND: An important concept in epidemiology is attributable risk, defined as the difference in risk between an exposed and an unexposed group. For example, in an intervention trial, the attributable risk is the difference in risk between a group that receives an intervention and another that does not. A fundamental assumption in estimating the attributable risk associated with the intervention is that disease outcomes are independent. When estimating population risks associated with treatment regimens designed to affect exposure to infectious pathogens, however, there may be bias due to the fact that infectious pathogens can be transmitted from host to host causing a potential statistical dependency in disease status among participants. METHODS: To estimate this bias, we used a mathematical model of community- and household-level disease transmission to explicitly incorporate the dependency among participants. We illustrate the method using a plausible model of infectious diarrheal disease. RESULTS: Analysis of the model suggests that this bias in attributable risk estimates is a function of transmission from person to person, either directly or indirectly via the environment. CONCLUSIONS: By incorporating these dependencies among individuals in a transmission model, we show how the bias of attributable risk estimates could be quantified to adjust effect estimates reported from intervention trials.     

Foodborne transmission of hepatitis A--Massachusetts, 2001

Hepatitis A virus (HAV) is transmitted typically from person to person by the fecal-oral route. Foodborne transmission occurs when an HAV-infected food handler contaminates food during preparation or when food is contaminated during harvesting or processing before reaching the food service establishment or home. Postexposure prophylaxis (PEP) with immune globulin (IG) can prevent hepatitis A among exposed persons if administered within 14 days of exposure. However, the decision about whether to implement PEP for persons who eat food prepared by an infected food handler depends on an assessment of the duties performed by the food handler and personal hygiene while potentially infectious, which are often difficult to determine. This report summarizes the investigation of an outbreak of foodborne hepatitis A in Massachusetts in which a food handler with hepatitis A, who was considered unlikely to transmit HAV, was implicated as the source. The findings underscore challenges faced by local and state health departments when determining whether PEP is appropriate.     

Development of an empirical model to aid in designing airborne infection isolation rooms

Airborne infection isolation rooms (AIIRs) house patients with tuberculosis, severe acute respiratory syndrome (SARS), and many other airborne infectious diseases. Currently, facility engineers and designers of heating, ventilation, and air-conditioning (HVAC) systems have few analytical tools to estimate a room's leakage area and establish an appropriate flow differential (DeltaQ) in hospitals, shelters, and other facilities where communicable diseases are present. An accurate estimate of leakage area and selection of DeltaQ is essential for ensuring that there is negative pressure (i.e., pressure differential [DeltaP]) between an AIIR and adjoining areas. National Institute for Occupational Safety and Health (NIOSH) researchers evaluated the relationship between DeltaQ and DeltaP in 67 AIIRs across the United States and in simulated AIIR. Data gathered in the simulated AIIR was used to develop an empirical model describing the relationship between DeltaQ, DeltaP, and leakage area. Data collected in health care facilities showed that the model accurately predicted the leakage area 44 of 48 times. Statistical analysis of the model and experimental validation showed that the model effectively estimated the actual leakage area from -39% to +22% with 90% confidence. The NIOSH model is an effective, cost-cutting tool that can be used by HVAC engineers and designers to estimate leakage area and select an appropriate DeltaQ in AIIRs to reduce the airborne transmission of disease.     

Modeling potential responses to smallpox as a bioterrorist weapon.

We constructed a mathematical model to describe the spread of smallpox after a deliberate release of the virus. Assuming 100 persons initially infected and 3 persons infected per infectious person, quarantine alone could stop disease transmission but would require a minimum daily removal rate of 50% of those with overt symptoms. Vaccination would stop the outbreak within 365 days after release only if disease transmission were reduced to <0.85 persons infected per infectious person. A combined vaccination and quarantine campaign could stop an outbreak if a daily quarantine rate of 25% were achieved and vaccination reduced smallpox transmission by > or = 33%. In such a scenario, approximately 4,200 cases would occur and 365 days would be needed to stop the outbreak. Historical data indicate that a median of 2,155 smallpox vaccine doses per case were given to stop outbreaks, implying that a stockpile of 40 million doses should be adequate.     

HIV infection risk to nonhealth-care workers

As has been summarized above, the risk of casual contact transmission of HIV virus is remote. A review of these data should provide reassurance to both workers and management. No evidence exists for direct contact spread through shaking hands and nonsexual touching. There is also no evidence for indirect spread through contact with shared inanimate objects such as typewriters, telephones, computers, water fountains, rest rooms, dining facilities, exercise equipment, bathing facilities, spas, saunas, and swimming pools. In addition, there is no evidence to suggest the airborne spread of HIV, thus there should be no potential risk of transmission through air-conditioning units, air-handling systems, or by sharing the same office space with an infected individual. The fear of AIDS may lead to irrational beliefs and biased perceptions of risk. This, unfortunately, can sometimes lead to discriminatory and inhumane treatment of persons with AIDS. The best way to manage this potential problem in the workplace is through effective educational interventions.     

对传染源定义的讨论和新冠病毒“物传人”理论基础的分析

目的 探讨被病原体污染的器物和环境可否认定为传染源,分析新型冠状病毒“物传人”的理论基础。方法 分析中、西方学术界对传染源定义的差异,回顾甲型肝炎、禽流感,重症急性呼吸综合征(SARS)等多种病毒性传染病“环境传人”和“物传人”的实例,运用生命科学的基本理论、基础知识,分析我国新型冠状病毒感染防控工作遇到的“进口冷链”“边贸或口岸作业”“国际邮件”等多种渠道传播新型冠状病毒的案例。结果 阐明我国对传染源定义严谨,强调可增殖性,只认可被病原体感染的人和动物为传染源;而西方的定义较宽泛,强调传染性,被病原体污染的器物和环境也可认定为传染源。通过理论分析和多方面实例证实新型冠状病毒在常温环境中存活期较长可至数天,在低温冷冻条件下存活期可延长至数月,被新型冠状病毒污染的器物可以引发间接接触感染,只是这种“物传人”的概率相对较低。结论 我国的传染源定义严谨、科学、实用,已在传染病防治工作中形成惯例,不宜改动。随着核酸检测技术的普及,新型冠状病毒感染等病毒性传染病筛查的目标可以从“快查传染源”转变为“快查病毒来源”,包括环境中的病毒。了解新型冠状病毒“物传人”理论基础,就理解了坚持“人物同防”等积...     

核事故辐射环境航空监测实例及思考

辐射环境航空监测具有快速、高效、覆盖面大的特点,是核事故应急监测中不可替代的重要技术手段。本文重点介绍了前苏联切尔诺贝利核电站核事故、美国三哩岛核电站核事故及日本福岛核电站核事故后开展的辐射环境航空监测行动。辐射环境航空监测技术在确定辐射污染范围、辐射环境调查及为国家相关部门快速提供技术支持方面发挥重要作用,是核事故应急响应行动中重要组成部分。建议有序开展核应急航空监测新型装备技术研究、核事故应急航空监测分析研判研究;有效应对核事故,开展全国核设施周围详细辐射环境水平摸底的航空监测研究。     

The risk of airborne influenza transmission in passenger cars

Travel in passenger cars is a ubiquitous aspect of the daily activities of many people. During the 2009 influenza A(H1N1) pandemic a case of probable transmission during car travel was reported in Australia, to which spread via the airborne route may have contributed. However, there are no data to indicate the likely risks of such events, and how they may vary and be mitigated. To address this knowledge gap, we estimated the risk of airborne influenza transmission in two cars (1989 model and 2005 model) by employing ventilation measurements and a variation of the Wells-Riley model. Results suggested that infection risk can be reduced by not recirculating air; however, estimated risk ranged from 59% to 99·9% for a 90-min trip when air was recirculated in the newer vehicle. These results have implications for interrupting in-car transmission of other illnesses spread by the airborne route.     

Norovirusinfektionen in Deutschland

Noroviruses are responsible for the majority of acute viral gastroenteritis infections worldwide. Transmission may be faecal-oral or through contaminated food and water or airborne by virus-containing aerosols. Characteristics of noroviruses that facilitate their spread are their high concentration in stool and vomitus, their extreme environmental stability, their low infectious dose as well as the lack of long-lasting immunity. The majority of norovirus infections occur in large outbreaks among persons living in institutional settings, such as hospitals and nursing homes, although sporadic cases also occur. Children and elderly persons are most often affected. Illness is characterized by acute onset of projectile vomiting. For prevention and control of norovirus outbreaks strict control management is necessary. Based on the high genomic variability new variant noroviruses with different pathogenic factors can arise. Depending on the circulating variant the extent of the usual winter peak can vary enormously. Available diagnostic methods include RT-PCR assays for detection of viral RNA, electron microscopy and enzyme immunoassays (EIA) for detection of viral antigens. The implicated virus can be subtyped through nucleotide sequencing and linked to a specific outbreak. With the enactment of the Protection against Infection Act in January 2001 a mandatory reporting system of norovirus infections was established. Analysis of surveillance data from this system permits a detailed overview of the nationwide epidemiology of this disease in Germany.     

春华秋实五十载悬壶济世一生情——庆贺王声湧教授执教50周年

我国著名的流行病学专家王声湧教授执教50周年庆典,于2011年6月18日在暨南大学隆重举行.暨南大学校长胡军教授等各级领导及王声湧教授的同事和学生代表200余人参加庆典活动.这也是我国流行病界同仁引以自豪的喜事.     

复杂网络模型在传染病预防控制中的应用

为探讨复杂网络模型在传染病预防控制中的应用,根据复杂网络的基本属性,利用网络模型和常用软件分析传染病传播过程.相对于传统的流行病学方法,复杂网络的理论不仅能描述传染病动态传播过程,也能进行传染病预测.通过复杂网络的理论来研究疾病的传播,能深入理解到网络的拓扑结构对疾病传播有重要影响,从而找到控制疾病传播的更有效的方法.