What techniques are recommended to undertake procedures that require asepsis? Content and cluster analysis of information supplied in international guidance.

BACKGROUND: Health professionals frequently conduct procedures requiring asepsis but there is no definitive evidence-based guidance on how aseptic technique should be undertaken. OBJECTIVE: To undertake content and cluster analysis to compare and contrast information relating to the conduct of aseptic technique in national and international guidance. METHODS: Content and hierarchical cluster analysis. RESULTS: We identified 16 sources of information from: organizations that generate infection prevention guidelines, provide advice about infection prevention in addition to other topics, generate guidance for procedures (e.g., wound care); practice manuals; MeSH and Wikipedia. Content related to: theory underpinning aseptic technique; terminology used; how and when it should be undertaken; and equipment. The nature and amount of information varied widely. Most frequently stated information related to: environment or equipment (N = 13), followed by the absolute nature of asepsis and the importance of hand hygiene (N = 10); general personal protective equipment, the significance of pathogens, and no-touch techniques (N = 8); that it is risk-based (N = 7); the existence of key parts or sites, and that there are different types of aseptic technique (N = 6). The most comprehensive sources were a wound care organization in the USA, and a British internationally used textbook. Least information was provided in some general infection prevention guidelines. CONCLUSION: Progress with research and practice in relation to aseptic technique suffers through lack of common goals and understanding. This study is one step towards establishing what constitutes aseptic technique, how and when it should be conducted, and the equipment necessary. This is required to support practice, policy and education, and may improve sustainability of healthcare resources.

Challenges undertaking procedures requiring asepsis: a qualitative interview study with nurses.

BACKGROUND: Invasive devices and breaches to skin and mucous membranes increase susceptibility to infection. Nurses frequently undertake procedures requiring asepsis (PRAs), but report challenges and unwarranted variations in practice. OBJECTIVE: To explore nurses' experiences, perceived gaps in information and support needed to conduct PRAs. METHODS: Qualitative interviews were undertaken with 20 nurses in the UK National Health Service between September 2021 and January 2022 employing approaches to sampling and data collection adopted in grounded theory. RESULTS: Informants were employed in diverse clinical settings. They thought that outside operating theatres, attempts to maintain asepsis would inevitably be compromised, but that much could still be done to contain the risk of contaminating susceptible sites irrespective of circumstances. Suboptimal practice was reported, and informants were unclear whether asepsis was needed to perform routine procedures (e.g. dressing chronic wounds, manipulating indwelling intravascular lines). Problems were attributed to inadequacies in nursing education, poor access to continuing professional development, and carelessness of junior nurses and medical staff. Informants wanted more detailed guidelines to conduct PRAs. Senior nurses wanted procedures to be conducted in the same way regardless of circumstance. Nurses who undertook PRAs regularly suggested that guidelines should be flexible. CONCLUSION: There is a need for detailed guidelines to inform PRAs, better access to clinical updating, and improvements in pre-registration nursing education. To meet contemporary standards, guideline generation should adopt recognized methodology. Student nurses should be introduced to the knowledge and skills required to undertake and adjust PRAs according to circumstance during simulated practice before contact with real patients.

Electronic hand hygiene monitoring systems can be well-tolerated by health workers: Findings of a qualitative study.

BACKGROUND: Electronic hand hygiene monitoring overcomes limitations associated with manual audit but acceptability to health workers varies and may depend on culture of the ward and the nature of the system. OBJECTIVES: Evaluate the acceptability of a new fifth type electronic monitoring system to frontline health workers in a National Health Service trust in the UK. METHODS: Qualitative interviews with 11 informants following 12 months experience using an electronic monitoring system. RESULTS: Informants recognised the importance of hand hygiene and embraced technology to improve adherence. Barriers to hand hygiene adherence included heavy workload, dealing with emergencies and ergonomic factors related to placement of alcohol dispensers. Opinions about the validity of the automated readings were conflicting. Some health workers thought they were accurate. Others reported problems associated with differences in the intelligence of the system and their own clinical decisions. Opinions about feedback were diverse. Some health workers thought the system increased personal accountability for hand hygiene. Others ignored feedback on suboptimal performance or ignored the data altogether. It was hard for health workers to understand why the system registered some instances of poor performance because feedback did not allow omissions in hand hygiene to be related to the context of care. CONCLUSION: Electronic monitoring can be very well tolerated despite some limitations. Further research needs to explore different reactions to feedback and how often clinical emergencies arise. Electronic and manual audit have complementary strengths.

The Hawthorne effect on adherence to hand hygiene in patient care.

Numerous studies demonstrate that the Hawthorne effect (behaviour change caused by awareness of being observed) increases health workers' hand hygiene adherence but it is not clear whether they are methodologically robust, what the magnitude of the effect is, how long it persists or whether it is the same across clinical settings. The objective of this review was to determine the rigour of the methods used to assess the Hawthorne effect on hand hygiene, effect size estimation, variations between clinical settings and persistence. To this end, a systematic literature review with meta-analysis was conducted. Nine studies met the criteria for the review. Methodological quality was variable. The Hawthorne effect ranged from -6.9% to 65.3%. It was 4.2% in one study conducted in intensive care and 16.4% in transplant units. It was most marked when data were collected across an entire hospital and in a group of general hospitals. Differences between wards in the same hospital were apparent. In the two studies where duration was estimated, the Hawthorne effect appeared transient. Despite methodological shortcomings, the review indicates clear evidence of a Hawthorne effect on general wards. There is evidence that it may vary between clinical speciality and across departments. The review identifies a need for standardized methodologies to measure the Hawthorne effect to overcome the dilemma of reporting the potentially inflated rates of adherence obtained through overt audit. Occasional covert audit could give a better estimation of true hand hygiene adherence but its acceptability and feasibility to health workers need to be explored.

Falciparum malaria: transmission to the gibbon by Anopheles balabacensis.

The splenectomized gibbon (Hylobates lar) is susceptible to sporozoite-induced infection by sporozoites of Plasmodium falciparum. Two gibbons inoculated with sporozoites of P. falciparum from Anopheles balabacensis fed on humans with falciparum malaria developed parasitemia 48 and 46 days after infection.

Repopulation of B-lymphocytes with restricted gene expression using haematopoietic stem cells engineered with lentiviral vectors.

B-lymphocytes play a key role in the pathogenesis of many immune-mediated diseases, such as autoimmune and atopic diseases. Therefore, targeting B-lymphocytes provides a rationale for refining strategies to treat such diseases for long-term clinical benefits and minimal side effects. In this study we describe a protocol for repopulating irradiated mice with B-lymphocytes engineered for restricted expression of transgenes using haematopoietic stem cells. A self-inactivating lentiviral vector, which encodes enhanced green fluorescence protein (EGFP) from the spleen focus-forming virus (SFFV) promoter, was used to generate new vectors that permit restricted EGFP expression in B-lymphocytes. To achieve this, the SFFV promoter was replaced with the B-lymphocyte-restricted CD19 promoter. Further, an immunoglobulin heavy chain enhancer (Emu) flanked by the associated matrix attachment regions (MARs) was inserted upstream of the CD19 promoter. Incorporation of the Emu-MAR elements upstream of the CD19 promoter resulted in enhanced, stable and selective transgene expression in human and murine B-cell lines. In addition, this modification permitted enhanced selective EGFP expression in B-lymphocytes in vivo in irradiated mice repopulated with transduced bone marrow haematopoietic stem cells (BMHSCs). The study provides evidence for the feasibility of targeting B-lymphocytes for therapeutic restoration of normal B-lymphocyte functions in patients with B-cell-related diseases.

Interventions to improve hand hygiene compliance in patient care.

Healthcare-associated infection is a major cause of morbidity and mortality. Hand hygiene is regarded as the most effective method of prevention but is poorly performed by health workers. We report a systematic review identifying studies which investigated the effectiveness of interventions to increase hand hygiene compliance short and longer term and to determine their success in terms of hand hygiene compliance and subsequent effect on rates of healthcare-associated infection. We employed the inclusion criteria employed by the Cochrane Effective Practice and Organisation of Care Group. Forty-eight studies and one thesis were identified. Only two met the stringent inclusion criteria. Overall studies remain small scale, poorly controlled and follow-up data collection is abandoned too soon to establish impact longer term. Furthermore, designs are insufficiently robust to attribute any observed changes to the intervention. Studies lack theoretical focus and seldom describe the intervention in sufficient detail, the change management process or contextual information about the organisation in the depth necessary to explain success or lack of it. The review concludes that interrupted time-series studies may offer the most rigorous approach to assessing the impact of interventions to increase hand hygiene compliance. In such study designs the number of new cases of healthcare-associated infection should be taken as an outcome measure, with data collection points at least 12 months before intervention and afterwards to allow for seasonal trends. Contextual factors at national and at local level should be carefully documented to take into consideration the influence of secular trends.

Changing the paradigm: messages for hand hygiene education and audit from cluster analysis.

BACKGROUND: Hand hygiene is considered to be the foremost infection prevention measure. How healthcare workers accept and make sense of the hand hygiene message is likely to contribute to the success and sustainability of initiatives to improve performance, which is often poor. METHODS: A survey of nurses in critical care units in three National Health Service trusts in England was undertaken to explore opinions about hand hygiene, use of alcohol hand rubs, audit with performance feedback, and other key hand-hygiene-related issues. Data were analysed descriptively and subjected to cluster analysis. RESULTS: Three main clusters of opinion were visualized, each forming a significant group: positive attitudes, pragmatism and scepticism. A smaller cluster suggested possible guilt about ability to perform hand hygiene. CONCLUSION: Cluster analysis identified previously unsuspected constellations of beliefs about hand hygiene that offer a plausible explanation for behaviour. Healthcare workers might respond to education and audit differently according to these beliefs. Those holding predominantly positive opinions might comply with hand hygiene policy and perform well as infection prevention link nurses and champions. Those holding pragmatic attitudes are likely to respond favourably to the need for professional behaviour and need to protect themselves from infection. Greater persuasion may be needed to encourage those who are sceptical about the importance of hand hygiene to comply with guidelines. Interventions to increase compliance should be sufficiently broad in scope to tackle different beliefs. Alternatively, cluster analysis of hand hygiene beliefs could be used to identify the most effective educational and monitoring strategies for a particular clinical setting.

Hand hygiene compliance monitoring in anaesthetics: Feasibility and validity.

BACKGROUND: Hand hygiene compliance scores in the anaesthetic department of an acute NHS hospital were persistently low. AIMS: To determine the feasibility and validity of regular accurate measurement of HHC in anaesthetics and understand the context of care delivery, barriers and opportunities to improve compliance. METHODS: The hand hygiene compliance of one anaesthetist was observed and noted by a senior infection control practitioner (ICP). This was compared to the World Health Organization five moments of hand hygiene and the organisation hand hygiene tool. FINDINGS: In one sequence of 55 min, there were approximately 58 hand hygiene opportunities. The hand hygiene compliance rate was 16%. The frequency and speed of actions in certain periods of care delivery made compliance measurement difficult and potentially unreliable. During several activities, taking time to apply alcohol gel or wash hands would have put the patients at significant risk. DISCUSSION: We concluded that hand hygiene compliance monitoring by direct observation was invalid and unreliable in this specialty. It is important that hand hygiene compliance is optimal in anaesthetics particularly before patient contact. Interventions which reduce environmental and patient contamination, such as cleaning the patient and environment, could ensure anaesthetists encounter fewer micro-organisms in this specialty.

Measuring handwashing performance in health service audits and research studies.

Handwashing is regarded as the most effective way of controlling healthcare-associated infection. A search of the literature identified 42 intervention studies seeking to increase compliance in which the data were collected by directly observing practice. The methods used to undertake observation were so poorly described in most studies that it is difficult to accept the findings as reliable or as valid indicators of health worker behaviour. Most studies were limited in scope, assessing the frequency of handwashing in critical care units. The ethical implications of watching health workers during close patient contact were not considered, especially when observation was covert or health workers were misinformed about the purpose of the study. Future studies should take place in a range of clinical settings to increase the generalizability of findings. Observation should be timed to capture a complete picture of 24h activity and should include all health workers in contact with patients because all have the potential to contribute to cross-infection. Reported details of observation should include: vantage of data collectors; inter-rater reliability when more than one individual is involved; and attempts to overcome the impact of observation on usual health worker behaviour. Ideally an additional data collection method should be used to corroborate or refute the findings of observation, but no well-validated method is presently available.

The CleanYourHandsCampaign: critiquing policy and evidence base.

Handwashing is considered to be the most effective way of reducing cross-infection. Rates of healthcare-associated infection and the incidence of meticillin-resistant Staphylococcus aureus are higher in the UK than in many other European countries. The government has responded by introducing the 'CleanYourHandsCampaign' throughout England and Wales, based on the success of the approach employed in Geneva. Alcohol hand rub is placed at every bedside in acute hospitals, ward housekeepers should replenish supplies and feedback on compliance is provided to health workers. Posters and other promotional materials are used to remind health workers and visitors to use the hand rub. Patients are encouraged to ask health workers if they have cleaned their hands before contact. In this paper we argue that the evidence base underpinning the CleanYourHandsCampaign is incomplete. Alcohol hand rub is acknowledged as a useful adjunct to hand hygiene but it is not effective in all circumstances. There is some evidence to support the use of feedback on performance to encourage compliance but no evidence that promotional materials such as posters or patient reminders are effective. The ethics of encouraging hospital patients to take responsibility for their own safety is questioned. Much of the success in Geneva must be attributed to the attention given to contextual factors within the organization that encouraged hand rub use, especially hospital-wide 'ownership' of the initiative by managers and senior health professionals. A customized intervention from another country that fails to consider local organizational factors likely to influence the implementation of the campaign is unlikely to be effective. It is concluded that although hand hygiene is of undoubted importance, undue emphasis should not be placed on it as a 'quick fix' to solve the unacceptably high rates of healthcare-associated infection in National Health Service hospitals.

Interventions to improve hand hygiene compliance in patient care.

BACKGROUND: Health care-associated infection is a major cause of morbidity and mortality. Hand hygiene is regarded as an effective preventive measure. OBJECTIVES: To assess the short and longer-term success of strategies to improve hand hygiene compliance and to determine whether a sustained increase in hand hygiene compliance can reduce rates of health care-associated infection. SEARCH STRATEGY: We conducted electronic searches of: the Cochrane Central Register of Controlled Trials; the Cochrane Effective Practice and Organisation of Care Group specialised register of trials; MEDLINE; PubMed; EMBASE; CINAHL; and the BNI. All databases were searched to July 2006; MEDLINE was searched from 1980, CINAHL from its inception, and the remainder from 1990 until July 2006. SELECTION CRITERIA: Randomised controlled trials; controlled clinical trials; controlled before and after studies; and interrupted time series analyses meeting explicit entry and quality criteria used by the Cochrane Effective Practice and Organisation of Care Group. Studies reporting proxy indicators of hand hygiene compliance were considered. Studies to promote compliance with universal precautions were included providing data relating specifically to hand hygiene were presented separately. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed data quality. MAIN RESULTS: Two studies met the criteria for review. One was a randomised controlled trial. The other was a controlled before and after study. Both were poorly controlled. Statistically significant post-intervention increase in hand washing was reported in one study up to four months after the intervention. In the other there was no post-intervention increase in hand hygiene compliance. AUTHORS' CONCLUSIONS: There is little robust evidence to inform the choice of interventions to improve hand hygiene. It appears that single interventions based on short, 'one off' teaching sessions are unlikely to be successful, even short-term. There is a need to undertake methodologically robust research to explore the effectiveness of soundly designed interventions to increase hand hygiene compliance.

Impact of observing hand hygiene in practice and research: a methodological reconsideration.

The purpose of hand hygiene is to break the chain of healthcare-associated infection. In many countries hand hygiene is regularly audited as part of quality assurance based on recommendations from the World Health Organization. Direct observation is the recommended audit method but is associated with disadvantages, including potential for being observed to alter usual behaviour. The Hawthorne effect in relation to hand hygiene is analogous with productivity improvement by increasing the frequency with which hand hygiene is undertaken. Unobtrusive and/or frequent observation to accustom staff to the presence of observers is considered an acceptable way of reducing the Hawthorne effect, but few publications have discussed how to implement these techniques or examine their effectiveness. There is evidence that awareness of being watched can disrupt the usual behaviour of individuals in complex and unpredictable ways other than simple productivity effect. In the presence of auditors, health workers might defer or avoid activities that require hand hygiene, but these issues are not addressed in guidelines for practice or research studies. This oversight has implications for the validity of hand hygiene audit findings. Measuring hand hygiene product use overcomes avoidance tactics. It is cheaper and generates data continuously to assess the compliance of all clinicians without disrupting patient care. Disadvantages are the risk of overestimating uptake through spillage, wastage, or use by visitors and non-clinical staff entering patient care areas. Electronic devices may overcome the Hawthorne and avoidance effects but are costly and are not widely used outside research studies.

Promoting health workers' ownership of infection prevention and control: using Normalization Process Theory as an interpretive framework.

BACKGROUND: All health workers should take responsibility for infection prevention and control (IPC). Recent reduction in key reported healthcare-associated infections in the UK is impressive, but the determinants of success are unknown. It is imperative to understand how IPC strategies operate as new challenges arise and threats of antimicrobial resistance increase. METHODS: The authors undertook a retrospective, independent evaluation of an action plan to enhance IPC and 'ownership' (individual accountability) for IPC introduced throughout a healthcare organization. Twenty purposively selected informants were interviewed. Data were analysed inductively. Normalization Process Theory (NPT) was applied to interpret the findings and explain how the action plan was operating. FINDINGS: Six themes emerged through inductive analysis. Theme 1: 'Ability to make sense of ownership' provided evidence of the first element of NPT (coherence). Regardless of occupational group or seniority, informants understood the importance of IPC ownership and described what it entailed. They identified three prerequisites: 'Always being vigilant' (Theme 2), 'Importance of access to information' (Theme 3) and 'Being able to learn together in a no-blame culture' (Theme 4). Data relating to each theme provided evidence of the other elements of NPT that are required to embed change: planning implementation (cognitive participation), undertaking the work necessary to achieve change (collective action), and reflection on what else is needed to promote change as part of continuous quality improvement (reflexive monitoring). Informants identified barriers (e.g. workload) and facilitators (clear lines of communication and expectations for IPC). CONCLUSION: Eighteen months after implementing the action plan incorporating IPC ownership, there was evidence of continuous service improvement and significant reduction in infection rates. Applying a theory that identifies factors that promote/inhibit routine incorporation ('normalization') of IPC into everyday health care can help explain the success of IPC initiatives and inform implementation.

Photodynamic therapy platform based on localized delivery of photosensitizer by vaterite submicron particles.

The elaboration of biocompatible and biodegradable carriers for photosensitizer targeted delivery is one of the most promising approaches in a modern photodynamic therapy (PDT). This approach is aimed at reducing sides effects connected with incidental toxicity in healthy tissue whilst also enhancing drug accumulation in the tumour area. In the present work, Photosens-loaded calcium carbonate (CaCO3) submicron particles in vaterite modification are proposed as a novel platform for anticancer PDT. Fast penetration of the carriers (0.9±0.2µm in diameter) containing 0.12% (w/w) of the photosensitizer into NIH3T3/EGFP cells is demonstrated. The captured particles provide the dye localization inside the cell increasing its local concentration, compared with "free" Photosens solution which is uniformly distributed throughout the cell. The effect of photosensitizer encapsulation into vaterite submicron particles on cell viability under laser irradiation (670nm, 19mW/cm(2), 10min) is discussed in the work. As determined by a viability assay, the encapsulation renders Photosens more phototoxic. By this means, CaCO3 carriers allow improvement of the photosensitizer effectiveness supposing, therefore, the reduction of therapeutic dose. Summation of these effects with the simplicity, upscalability and cheapness of fabrication, biocompatibility and high payload ability of the vaterite particles hold out the prospect of a novel PDT platform.

Working practices and success of infection prevention and control teams: a scoping study.

Little research has been undertaken on how infection prevention and control (IPC) teams operate and how their effectiveness is assessed. This review aimed to explore how IPC teams embed IPC throughout hospitals, balance outbreak management with strategic aspects of IPC work (e.g. education), and how IPC team performance is measured. A scoping exercise was performed combining literature searches, evidence synthesis, and intelligence from expert advisers. Eleven publications were identified. One paper quantified how IPC nurses spend their time, two described daily activities of IPC teams, five described initiatives to embed IPC across organizations following legislation since 1999 in the UK or changes in the delivery of healthcare, and three explored the contribution of IPC intermediaries (link nurses and champions). Eight publications reported research findings. The others reported how IPC teams are embedding IPC practice in UK hospitals. In conclusion, there is scope for research to explore different models of IPC team-working and effectiveness, and cost-effectiveness. Other topics that need addressing are the willingness and ability of ward staff to assume increased responsibility for IPC and the effectiveness of intermediaries.

Collecting the data but missing the point: validity of hand hygiene audit data.

BACKGROUND: Monitoring of hand hygiene compliance (HHC) by observation has been used in healthcare for more than a decade to provide assurance of infection control practice. The validity of this information is rarely tested. AIM: To examine the process and validity of collecting and reporting HHC data based on direct observation of compliance. METHODS: Five years of HHC data routinely collected in one large National Health Service hospital trust were examined. The data collection process was reviewed by survey and interview of the auditors. HHC data collected for other research purposes undertaken during this period were compared with the organizational data set. FINDINGS: After an initial increase, the reported HHC remained unchanged close to its intended target throughout this period. Examination of the data collection process revealed changes, including local interpretations of the data collection system, which invalidated the results. A minority of auditors had received formal training in observation and feedback of results. CONCLUSION: Whereas observation of HHC is the current gold standard, unless data collection definitions and methods are unambiguous, published, carefully supervised, and regularly monitored, variations may occur which affect the validity of the data. If the purpose of HHC monitoring is to improve practice and minimize transmission of infection, then a focus on progressively improving performance rather than on achieving a target may offer greater opportunities to achieve this.

Cross talk between receptors mediating contraction and relaxation in the arterioles but not the dilator muscle of the rat iris.

1. Sympathetic nerve stimulation causes contraction of the dilator muscle and the large arterioles of the iris via the activation of alpha 1B-adrenoceptors. We have investigated whether increases in adenosine 3': 5'-cyclic monophosphate (cyclic AMP) and the activation of receptors in these tissues can modulate these nerve-mediated contractions. 2. Increasing intracellular cyclic AMP with dibutyryl cyclic AMP (1 mM), forskolin (50 microM) or isobutylmethylxanthine (100 microM) produced relaxation of both the dilator and the arterioles, abolished the nerve-mediated constriction of the arterioles, but potentiated the nerve-mediated contraction of the iris dilator. 3. Pretreatment of the preparations with cholera toxin, to activate Gs permanently, caused a dilatation of the arterioles and abolished the nerve-mediated constriction but had no effect on the dilator muscle. 4. The beta-adrenoceptor agonist, isoprenaline (1 microM), the adenosine-A1,-A2 agonist, N-ethylcarboxamidoadenosine NECA (100 nM), in the presence of the A1-selective antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 10 nM), and calcitonin gene-related peptide (CGRP, 10 nM) all separately caused a dilatation of the arterioles and abolished the nerve-mediated constriction, while only isoprenaline (1 microM) produced an effect on the dilator, i.e. a relaxation but a potentiation of the nerve-mediated contraction. These results suggest the presence of at least 3 types of receptor linked to Gs and an increase in cyclic AMP in the arterioles, i.e. beta-adrenoceptor, adenosine-A2 and CGRP, but only 1 Gs-linked receptor, i.e. beta-adrenoceptors, on the dilator muscle cells.2+ '

Isolation of Langat virus from Haemaphysalis papuana Thorell in Thailand.

A strain of Langat virus (LGT), T-1674, was isolated from a pool of Haemaphysalis papuana Thorell collected in the forest of Khao Yai National Park in Central Thailand. The isolated virus was found to have growth and antigenic similarity to the prototype Langat strain (TP-21). This is the first report of a natural infection of Haemaphysalis ticks with LGT and of the isolation of this arbovirus in Thailand. The wide distribution of known vectors of LGT in Thailand suggests that the virus may be present in other areas of the country.

Dengue-2 vaccine: infection of Aedes aegypti mosquitoes by feeding on viremic recipients.

Colonized Aedes aegypti mosquitoes were fed on voluntary recipients of an experimental, live, attenuated, dengue type 2 (PR 159/S-1) vaccine to estimate the frequency of vector infection and the stability of the virus in mosquitoes. Two volunteers were viremic at the time of mosquito feeding, but only two of 114 mosquitoes that took a viremic blood meal became infected with the vaccine virus. Strains of virus recovered from the bodies of the mosquitoes and the volunteer's blood retained the temperature sensitivity and small plaque growth characteristics of the vaccine virus. Dengue viral antigen was not detectable in any of the mosquito heads by direct immunofluorescence and in vitro virus transmission by droplet feeding was not observed. This experiment showed that vector mosquitoes can be infected with vaccine virus by feeding on viremic vaccinees. Furthermore, the virus is sufficiently stable to retain the in vitro growth characteristics associated with the vaccine virus.