Risk Assessment Of Transmission Research Articles

Effect of meteorological factors on clinical malaria risk among children: an assessment using village-based meteorological stations and community-based parasitological survey

BackgroundTemperature, rainfall and humidity have been widely associated with the dynamics of malaria vector population and, therefore, with spread of the disease. However, at the local scale, there is a lack of a systematic quantification of the effect of these factors on malaria transmission. Further, most attempts to quantify this effect are based on proxy meteorological data acquired from satellites or interpolated from a different scale. This has led to controversies about the contribution of climate change to malaria transmission risk among others. Our study addresses the original question of relating meteorological factors measured at the local scale with malaria infection, using data collected at the same time and scale.Methods676 children (6–59 months) were selected randomly from three ecologically different sites (urban and rural). During weekly home visits between December 1, 2003, and November 30, 2004, fieldworkers tested children with fever for clinical malaria. They also collected data on possible confounders monthly. Digital meteorological stations measured ambient temperature, humidity, and rainfall in each site. Logistic regression was used to estimate the risk of clinical malaria given the previous month's meteorological conditions.ResultsThe overall incidence of clinical malaria over the study period was 1.07 episodes per child. Meteorological factors were associated with clinical malaria with mean temperature having the largest effect.ConclusionTemperature was the best predictor for clinical malaria among children under five. A systematic measurement of local temperature through ground stations and integration of such data in the routine health information system could support assessment of malaria transmission risk at the district level for well-targeted control efforts.

Risk assessment of transmission of bovine viral diarrhea virus (BVDV) in abattoir-derived in vitro produced embryos

Bovine virus diarrhea virus (BVDV) is a pathogen of the bovine reproductive system causing reduced conception rates, abortions and persistently infected calves. Most if not all strains of BVDV are transmissible by natural mating and AI. For international trade, it is recommended that in vitro fertilized embryos be washed according to the IETS Manual. However, BVDV may not be entirely washed out, resulting in possible transmission risks to recipients. Donor cows, donor bulls and biological agents are all possible sources of contamination. The process for producing in vitro produced (IVP) embryos is complex and non-standard, and some procedures can contribute to spread of BVDV to uninfected embryos. The structure of the zone pellucida (ZP) of IVP embryos permits adherence of BVDV to the ZP. To estimate the risk of producing infected recipients and persistently infected calves from abattoir-derived IVP embryos, a quantitative risk assessment model using Microsoft Excel ® and Palisade @Risk ® was developed. Assumptions simplified some of the complexities of the IVP process. Uncertainties due to incomplete or variable data were addressed by incorporating probability distributions in the model. Model variables included: disease prevalence; the number of donor cows slaughtered for ovaries; the number of oocytes collected, selected and cultured; the BVDV status of ovaries, semen, biological compounds and its behavior in the IVP embryo process. The model used the Monte Carlo method to simulate the IVP process. When co-culture cells derived from donor cows of unknown health status were used for in vitro culture (IVC), the probability of a recipient cow at risk of infection to BVDV per oocyte selected for IVP processing averaged 0.0006. However, when co-culture free from BVDV was used, the probability was 1.2 × 10 −5. Thus, for safe international trade in bovine IVP embryos (i.e. negligible risks of transmission of BVDV), co-culture cells, if used during IVC for producing IVP embryos, should be disease-free.

O246 Risk assessment and management of possible transmission of Lassa virus during two flights

Crimean-Congo haemorrhagic fever (CCHF) virus is a tick-borne member of the genus Nairovirus, family Bunyaviridae. CCHF virus has been isolated from at least 31 different species of ticks. The virus is transmitted through the bite of an infected tick or by direct contact with CCHF virus-infected patients or the products of infected livestock. This study was conducted to determine the rate of CCHF virus infection in ticks in the district of Zahedan, in the province of Sistan and Baluchistan, southeastern Iran. A total of 140 ticks were collected from Sistan and Baluchistan. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used for the detection of the CCHF virus genome in the tick population. This genome was detected in 4.3% of ticks collected from livestock of different regions of Zahedan. The infected tick genera belonged to Hyalomma and Haemaphysalis. Although in the epidemiology of CCHF virus Hyalomma ticks are considered to be the most important vectors and reservoirs, the virus has also been reported to occur in other genera of ticks, which conforms to the current data in our study from Sistan and Baluchistan. Given that animals are common hosts for Hyalomma and Haemaphysalis, regular monitoring programmes for livestock should be applied for CCHF virus control.

Epidemiologic investigation of a cluster of workplace HIV infections in the adult film industry: Los Angeles, California, 2004.

Adult film production is a legal, multibillion dollar industry in California. In response to reports of human immunodeficiency virus (HIV) transmission by an adult film worker, we sought to determine the extent of HIV infection among exposed workers and to identify means of improving worker safety. The Los Angeles County Department of Health Services initiated an outbreak investigation that included interviews of infected workers to elicit information about recent sex partners, review of the testing agency's medical records and laboratory results, molecular analysis of HIV isolates from the 4 infected workers, and a risk assessment of HIV transmission in the adult film industry. Many adult film workers participate in a monthly program of screening for HIV infection by means of polymerase chain reaction-based technology to detect HIV DNA in blood. A male performer tested negative for HIV on 12 February 2004 and 17 March 2004, then tested positive for HIV on 9 April 2004. During the period between the negative test results, he experienced a flulike illness after performing unprotected vaginal and anal intercourse for an adult film produced outside the United States by a US company. After returning to California, he performed unprotected sex acts for adult films with 13 female partners who had all tested negative for HIV in the preceding 30 days; 3 subsequently tested positive for HIV (a 23% attack rate). Contact tracing identified no reasonable sources of infection other than the male index patient. Although current testing methods may shorten the window period to diagnosis of new HIV infection, they fail to prevent occupational acquisition of HIV in this setting. A California Occupational Safety and Health Administration-approved written health and safety program that emphasizes primary prevention is needed for this industry.

Dimensions of engorging Ixodes ricinus as a measure of feeding duration

Knowledge of the duration of tick feeding can contribute to assessment of disease transmission risk, and may be estimated from changes in body dimensions during engorgement. Application of this approach to the European tick, Ixodes ricinus, is described here. Nymphal and adult female I. ricinus ticks were detached at predetermined intervals from laboratory rabbits and their state of engorgement estimated by calculating either the scutal index (the ratio of the width of the scutum to the length of the idiosoma) or the coxal index (the ratio of the width of the scutum to the distance between the basal coxae of the fourth pair of legs – the coxal gap). The coxal index proved to be more accurate in estimating duration of feeding over the first 24 h, but the scutal index was more accurate later in feeding. The coxal index may be used in combination with the scutal index to estimate the period of time that ticks removed from patients have been feeding, thus assisting with the assessment of pathogen transmission risk.

Infection transmission risk assessment tool for nursing to determine transmission-based precautions upon admission

ISSUE: At this acute care facility, the responsibility of assigning patients to isolation, unless ordered by the physician, often became the responsibility of the infection control practitioner (ICP). As the ICP performs surveillance using data such as microbiology results or admitting diagnosis, there was a time lag for proper placement of patients for transmission-based precautions. PROJECT: An infection transmission risk assessment (ITRA) tool was created on the nursing admission assessment form incorporating Centers for Disease Control and Prevention (CDC) Guidelines for Isolation Precautions in Hospitals. The infection prevention committee approved the ITRA tool. The medical executive team empowered nurses to isolate patients based upon this assessment or physician diagnosis. All nurses in orientation are introduced to the ITRA tool. During the annual nursing competency, recent cases are used to illustrate proper isolation category. Appendix A from the CDC isolation guidelines was made available for easy reference on specific diseases. A daily worksheet with isolation patients prints on each inpatient station to improve communication and accountability for isolation after an isolation task force identified this as an opportunity. The task force was a multidisciplinary team that met weekly or biweekly in 2003 to address communication and process problems related to isolation. RESULTS: The ITRA tool became part of the nursing admission form in 2001. However, only 60% of patients were assessed for isolation in 2002. In 2004, 97.3% of patients were correctly isolated. Proper isolation codes in the computer system improved dramatically (0% in 2002 versus 94% in 2004). An increase in medical discrepancies for isolation errors occurred (51 in 2002, 78 in 2003, 102 in 2004), showing the heightened awareness about isolation needs. LESSONS LEARNED: The ITRA tool by itself was not enough to improve isolation; it required frequent education and wide support. The task force identified and developed processes to reduce isolation problems and encouraged the environmental climate to effect change. The multidisciplinary team, not the tool, made the difference.

Quantitative Risk Assessment of FMD Virus Transmission via Water

Foot-and-mouth disease (FMD) is a viral disease of domesticated and wild cloven-hoofed animals. FMD virus is known to spread by direct contact between infected and susceptible animals, by animal products such as meat and milk, by the airborne route, and mechanical transfer on people, wild animals, birds, and by vehicles. During the outbreak of 2001 in the Netherlands, milk from dairy cattle was illegally discharged into the sewerage as a consequence of transport prohibition. This may lead to contaminated discharges of biologically treated and raw sewage in surface water that is given to cattle to drink. The objective of the present study was to assess the probability of infecting dairy cows that were drinking FMD virus contaminated surface water due to illegal discharges of contaminated milk. So, the following data were collected from literature: FMD virus inactivation in aqueous environments, FMD virus concentrations in milk, dilution in sewage water, virus removal by sewage treatment, dilution in surface water, water consumption of cows, size of a herd in a meadow, and dose-response data for ingested FMD virus by cattle. In the case of 1.6 x 10(2) FMD virus per milliliter in milk and discharge of treated sewage in surface water, the probability of infecting a herd of cows was estimated to be 3.3 x 10(-7) to 8.5 x 10(-5), dependent on dilution in the receiving surface water. In the case of discharge of raw sewage, all probabilities of infection were 100 times higher. In the case of little dilution in small rivers, the high level of 8.5 x 10(-3) is reached. For 10(4) times higher FMD virus concentrations in milk, the probabilities of infecting a herd of cows are high in the case of discharge of treated sewage (3.3 x 10(-3) to 5.7 x 10(-1)) and very high in the case of discharge of raw sewage (0.28-1.0). It can be concluded that illegal and uncontrolled discharges of contaminated milk into the sewerage system may lead to high risks to other cattle farms at 6-50 km distance of the location of discharge within one day. This clearly underlines current measures that prohibit such discharges, and also asks for strict control. This risk assessment clearly demonstrated the potential significance of FMD virus transmission via water, and the results will be useful on an international scale, and could also serve as a basis for other FMD risk-assessment models.

Biological diversity versus risk for mosquito nuisance and disease transmission in constructed wetlands in southern Sweden.

In southern Sweden, many wetlands have been constructed, and maintaining or increasing biological diversity is often included in the aims. Some wetlands are constructed near human settlements, thus raising the problem of wetlands being associated with mosquitoes (Diptera: Culicidae). Increased biodiversity (including mosquito diversity) is considered desirable, whereas mosquito nuisance from a human point of view is not. Adult mosquito abundance, diversity and species assemblages of constructed wetlands were compared to natural wetlands. The potential of constructed wetlands for mosquito nuisance and transmission of mosquito-borne viruses was evaluated. The study areas included five constructed and four natural wetlands. Mosquito abundance and species richness were higher in the natural than in the constructed wetlands, and showed a positive correlation with wetland size. Mosquito species assemblages formed three clusters, which were not explained by origin, size and water permanence of wetlands. In a redundancy analysis, however, mosquito faunas showed significant relationships with these variables, and size and origin of wetlands were most important. Major nuisance species (multivoltine species feeding on mammals and laying eggs on soil) were found in all wetlands, although in relatively low numbers. Risk assessment for Sindbis virus transmission showed moderate risk for two constructed wetlands near human settlements. It is concluded that small size of constructed wetlands has the advantage of low mosquito numbers from a human point of view. The use of functional groups is recommended as a tool for presenting mosquito data to the public, and for helping communication between scientists and administrative decision makers.

Aspects of risk assessment and risk management of nosocomial transmission of classical and variant Creutzfeldt-Jakob disease with special attention to German regulations.

Aspects of risk assessment and risk management of nosocomial transmission of classical and variant Creutzfeldt-Jakob disease with special attention to German regulations.

Studies of Quantitative Parameters of Virus Excretion and Transmission in Pigs and Cattle Experimentally Infected with Foot-and-Mouth Disease Virus

Foot-and-mouth disease virus (FMDV) can be spread by a variety of mechanisms and the rate of spread, the incubation period and the severity of disease depend on a multitude of parameters, including the strain of virus, the dose received, the route of introduction, the animal species and the husbandry conditions. More knowledge with regard to these parameters is urgently needed to improve resource-efficient disease control. This report describes detailed studies of FMDV load, excretion and transmission in pigs infected with FMDV O UKG 2001, O TAW 1997 and C Noville virus and in cattle infected with the O UKG 2001 virus to facilitate use of a “FMDV load framework” for the assessment of transmission risks. Virus replicated rapidly in pigs and cattle exposed by direct contact. The mean incubation period was around 3–4 days for cattle-to-cattle and 1–3 days for pig-to-pig transmission, depending on the intensity of contact. The results confirmed that a strong relation exists between dose and length of incubation period. Clinical disease was severe in pigs but relatively mild in inoculated cattle; contact infection of cattle appeared to increase the severity of lesions. FMDV RNA was recovered in nasal and mouth swabs from inoculated animals soon after they developed a viraemia and probably reflected the early production and excretion of virus. FMDV RNA in nasal and mouth swabs from contact animals could be detected several days before they showed other signs of infection, indicating the possibility of detecting exposed animals during the incubation period. FMDV RNA could also be detected in swab samples after the viraemic phase. This may have represented background environmental virus that had been trapped in the respiratory tract and mouth. Alternatively, it may have indicated a somewhat slower clearance or half-life of viral RNA or an extended low level of FMDV replication at these sites. The pattern of FMDV RNA concentrations in pigs was closely similar to that in cattle, but the amounts of FMDV RNA were higher.

Meteorologically mediated diurnal questing of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) nymphs.

Questing Ixodes scapularis Say and Amblyomma americanum (L.) nymphs were collected in the field by drag sampling to determine whether ticks would be collected in greater numbers during certain times of the day and under certain ambient meteorological conditions. Ticks were collected hourly for 16 h on 4 d and counts were contrasted with simultaneous measurements of ambient temperature and relative humidity, and with similar measurements made within the leaf litter. Peak numbers of questing I. scapularis and A. americanum nymphs were collected at distinctly different times of day, suggesting that the two species were responding to different environmental conditions. Both species demonstrated responses to diel changes in local meteorological conditions. Numbers of ticks were correlated with ambient temperature and humidity and with conditions recorded in the leaf litter that appeared to play a significant role in mediating questing behavior of both species. The time of day when tick sampling is conducted might significantly bias population estimates for sympatric species and the assessment of tick-borne disease transmission risk.

Psychometric properties of the Blood-borne Virus Transmission Risk Assessment Questionnaire (BBV-TRAQ).

To develop a standard measure of blood-borne virus transmission risk behaviour, and examine the underlying psychometric properties. The Blood-borne Virus Transmission Risk Assessment Questionnaire (BBV-TRAQ) was developed over three consecutive phases of the original BBV-TRAQ study in adherence to classical scale development procedures, culminating in the recruitment of a development sample of current injecting drug users via convenience and snowball sampling. Needle and syringe programmes (NSPs), medical clinics, alcohol/drug agencies, peer-based and outreach organizations across inner and outer metropolitan Melbourne. Two hundred and nine current injecting drug users. The mean age was 27 years, 68% were male, 65% unemployed, 36% with prison history and 25% in methadone maintenance. BBV-TRAQ items cover specific injecting, sexual and skin penetration risk practices. BBV-TRAQ characteristics were assessed via measures of internal and test-retest reliability; collateral validation; and principal components analyses. The BBV-TRAQ has satisfactory psychometric properties. Internal (a=0.87), test-retest (r=0.84) and inter-observer reliability results were high, suggesting that the instrument provides a reliable measure of BBV risk behaviour and is reliable over time and across interviewers. A principal components analysis with varimax rotation produced a parsimonious factor solution despite modest communality, and indicated that three factors (injecting, sex and skin penetration/hygiene risks) are required to describe BBV risk behaviour. The BBV-TRAQ is reliable and represents the first risk assessment tool to incorporate sufficient coverage of injecting, sex and other skin penetration risk practices to be considered truly content valid. The questionnaire is indicated for use in addictions research, clinical, peer education and BBV risk behaviour surveillance settings.

Poor assessment of HIV epidemiology and occupational HIV transmission risk by medical students

Due to the increasing global number of HIV-positive patients, the potential risk of acquiring infection with HIV during routine clinical care is on the increase. Assessments of the knowledge of medical students about occupational HIV transmission are therefore important. This study analysed the knowledge of 397 first year and 75 fifth year medical students about the epidemiology of HIV in Germany and their assessment of the risk of acquiring HIV in different clinical situations. Medical students overestimated the incidence and mortality of HIV in Germany, with fewer than 30% knowing the correct numbers. They also overestimated the risk of occupational HIV infection in several clinical settings, such as changing dirty linen or wound dressings. Few differences were found between first and fifth year medical students. For their later work as physicians medical students still need more information and counselling about the epidemiology of HIV, prevention of occupational HIV infections and care for patients with HIV/AIDS.

Effects of selected meterological factors on diurnal questing of Ixodes scapularis and Amblyomma Americanum (Acari: Ixodidade).

The diurnal questing behavior of adult Ixodes scapularis Say and Amblyomma americanum (L.) were monitored in the field to determine whether ticks would be collected with greater frequency during certain times of the day and under certain ambient meteorological conditions. Temperature and relative humidity explained a significant amount of the total variation in tick collections. Although both species were collected during every period, I. scapularis adults tended to quest earlier and later in the day when temperatures were lower and relative humidity higher, whereas A. americanum were collected with greater frequency in late morning and early afternoon during periods of higher temperatures and lower humidity. Questing of I. scapularis adults was observed at temperatures as low as -0.6 degrees C, whereas no adult A. americanum were collected below 4.4 degrees C. The questing temperature threshold for I. scapularis adults observed in this study was below that reported previously. The implications of these temporal activity patterns on the assessment of disease transmission risk and sampling bias are also discussed.

Assessment of HIV transmission risks in clinical situations in health care students from Germany, Lithuania and Namibia

Due to the increasing global HIV prevalence, comprehensive knowledge about clinical HIV transmission risks in health care professionals is essential. Mainly medical and nursing students are at risk, because they are working close to infected patients. By using an anonymous questionnaire, the study analysed the assessments of German medical/dental students ( n=182), Lithuanian medical students ( n=176) and Namibian student nurses ( n=135) on the risk of getting HIV infected in different clinical situations. It became obvious that the Namibian student nurses overestimated the risk of HIV transmission in several situations (eg changing dirty linen, physical examination). In comparison, the Lithuanian students showed the most realistic assessments, while the German students also tended to overestimate the risks of HIV transmission. The results indicate that assessments on the risk of HIV transmission in clinical situations are influenced by the national prevalence and daily contacts with HIV patients. Education of health care students should consider this and focus more on epidemiological aspects and infection control procedures, to avoid endangering students and patients. Public Health (2001) 115, 114–118

Assessment of HIV transmission risks in clinical situations in health care students from Germany, Lithuania and Namibia

Due to the increasing global HIV prevalence, comprehensive knowledge about clinical HIV transmission risks in health care professionals is essential. Mainly medical and nursing students are at risk, because they are working close to infected patients. By using an anonymous questionnaire, the study analysed the assessments of German medical/dental students (n=182), Lithuanian medical students (n=176) and Namibian student nurses (n=135) on the risk of getting HIV infected in different clinical situations. It became obvious that the Namibian student nurses overestimated the risk of HIV transmission in several situations (eg changing dirty linen, physical examination). In comparison, the Lithuanian students showed the most realistic assessments, while the German students also tended to overestimate the risks of HIV transmission. The results indicate that assessments on the risk of HIV transmission in clinical situations are influenced by the national prevalence and daily contacts with HIV patients. Education of health care students should consider this and focus more on epidemiological aspects and infection control procedures, to avoid endangering students and patients. Public Health (2001) 115, 114–118

Infection of nonhuman primate cells by pig endogenous retrovirus.

The ongoing shortage of human donor organs for transplantation has catalyzed new interest in the application of pig organs (xenotransplantation). One of the biggest concerns about the transplantation of porcine grafts into humans is the transmission of pig endogenous retroviruses (PERV) to the recipients or even to other members of the community. Although nonhuman primate models are excellently suited to mimic clinical xenotransplantation settings, their value for risk assessment of PERV transmission at xenotransplantation is questionable since all of the primate cell lines tested so far have been found to be nonpermissive for PERV infection. Here we demonstrate that human, gorilla, and Papio hamadryas primary skin fibroblasts and also baboon B-cell lines are permissive for PERV infection. This suggests that a reevaluation of the suitability of the baboon model for risk assessment in xenotransplantation is critical at this point.

The role of the toxicologic pathologist in the preclinical safety evaluation of biotechnology-derived pharmaceuticals.

Biotechnology-derived pharmaceuticals, or biopharmaceuticals, represent a special class of complex, high molecular weight products, such as monoclonal antibodies, recombinant proteins, and nucleic acids. With these compounds, it is not appropriate to follow conventional safety testing programs, and the preclinical "package" for each biopharmaceutical needs to be individually designed. In addition to standard histopathology, the use of molecular pathology techniques is often required either in conventional animal studies or in in vitro tests. In this review, the safety evaluation of biopharmaceuticals is discussed from the perspective of the toxicologic pathologist, and appropriate examples are given of the use of molecular pathology procedures. Examples include the use of in situ hybridization to localize gene therapy vectors, the assessment of vector integration into genomic DNA by the polymerase chain reaction (PCR), and the use of immunohistochemistry to evaluate the potential cross-reactivity of monoclonal antibodies. In situ PCR techniques may allow for confirmation of the germ cell localization of nucleic acids and may therefore facilitate the risk assessment of germline transmission. Increased involvement with biopharmaceuticals will present challenging opportunities for the toxicologic pathologist and will allow for much greater use of molecular techniques, which have a critical role in the preclinical development of these compounds.

Risk assessment of bovine spongiform encephalopathy transmission through bone graft material derived from bovine bone used for dental applications.

Several commercial products are currently available for clinical application as bone graft substitutes. These products can be broadly classified into two categories: synthetic and natural. Bovine bone is a popular source for several of the natural bone substitutes. The availability of bovine derived xenogenic bone substitutes has made it possible to avoid traumatic and expensive secondary surgery to obtain autogenous bone once thought essential for effective bone replacement. While autogenous bone still remains the undisputed "gold standard" in bone grafting, the realization that bone requirement in several clinical applications is as effectively met by xenografts has lead to their widespread use. But the convenience of using xenografts is tempered by the possibility of disease transmission from cattle to humans. The recent incidents of bovine spongiform encephalopathies (BSE) in humans have underscored this likelihood. In this paper, we report a risk analysis performed to assess the possibility of such disease transmission from a commercially available bone graft substitute (BGS) that is popularly used in clinical dentistry. An extensive review of current literature on the status of risk assessment of BSE transmission was conducted, and two risk assessment models were identified as applicable to the present study. Risk assessment models developed by the German Federal Ministry of Health and by the Pharmaceutical Research and Manufacturers Association of America were applied to BGS. Results from the analyses conducted using both models showed that the risk of disease (BSE) transmission from BGS was negligible and could be attributed to the stringent protocols followed in sourcing and processing of the raw bovine bone used in the commercial product. Based on the risk analysis, it is evident that the risk of BSE infection from BGS is several orders of magnitude less than that posed by the risk of death related to, lightning, tornadoes, or similar remote events. However, this low risk can only be maintained as long as an effective and active risk management program is implemented in operations that involve processing xenogenic tissue for human use.

Effect of size and geographic origin of Aedes aegypti on oral infection with dengue-2 virus.

Differences in larval habitats cause variation in the size of Aedes aegypti (L.) adults. We suspected that such size variation was related to the ease with which the mosquitoes could be infected with dengue virus. Using a rearing procedure that produced three distinct size classes of mosquitoes, we determined the percentage of mosquitoes that developed disseminated dengue-2 infection following oral feeding with a suspension containing 3.3 x 10(7) plaque-forming units/ml. Mosquitoes were reared from eggs deposited by females captured in either of two villages in Chachoengsao Province or in Bangkok, Thailand. More of the larger mosquitoes (10.7%) were infected than the medium (5.6%) or small (5.7%) mosquitoes. Mosquitoes from Bangkok were less easily infected (5.0%) than mosquitoes from either of the two villages (8.5% and 10.7%). These results suggest that quantitative risk assessment of dengue transmission may be very difficult unless inoculation rate is measured directly. Also, control procedures that reduce density of larvae in individual containers may exacerbate dengue transmission by creating larger mosquitoes that are more easily infected.