Publisher Correction: Malaria predictions based on seasonal climate forecasts in South Africa: A time series distributed lag nonlinear model.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Malaria predictions based on seasonal climate forecasts in South Africa: A time series distributed lag nonlinear model.

Although there have been enormous demands and efforts to develop an early warning system for malaria, no sustainable system has remained. Well-organized malaria surveillance and high-quality climate forecasts are required to sustain a malaria early warning system in conjunction with an effective malaria prediction model. We aimed to develop a weather-based malaria prediction model using a weekly time-series data including temperature, precipitation, and malaria cases from 1998 to 2015 in Vhembe, Limpopo, South Africa and apply it to seasonal climate forecasts. The malaria prediction model performed well for short-term predictions (correlation coefficient, r > 0.8 for 1- and 2-week ahead forecasts). The prediction accuracy decreased as the lead time increased but retained fairly good performance (r > 0.7) up to the 16-week ahead prediction. The demonstration of the malaria prediction process based on the seasonal climate forecasts showed the short-term predictions coincided closely with the observed malaria cases. The weather-based malaria prediction model we developed could be applicable in practice together with skillful seasonal climate forecasts and existing malaria surveillance data. Establishing an automated operating system based on real-time data inputs will be beneficial for the malaria early warning system, and can be an instructive example for other malaria-endemic areas.

Seasonally lagged effects of climatic factors on malaria incidence in South Africa.

Globally, malaria cases have drastically dropped in recent years. However, a high incidence of malaria remains in some sub-Saharan African countries. South Africa is mostly malaria-free, but northeastern provinces continue to experience seasonal outbreaks. Here we investigate the association between malaria incidence and spatio-temporal climate variations in Limpopo. First, dominant spatial patterns in malaria incidence anomalies were identified using self-organizing maps. Composite analysis found significant associations among incidence anomalies and climate patterns. A high incidence of malaria during the pre-peak season (Sep-Nov) was associated with the climate phenomenon La Niña and cool air temperatures over southern Africa. There was also high precipitation over neighbouring countries two to six months prior to malaria incidence. During the peak season (Dec-Feb), high incidence was associated with positive phase of Indian Ocean Subtropical Dipole. Warm temperatures and high precipitation in neighbouring countries were also observed two months prior to increased malaria incidence. This lagged association between regional climate and malaria incidence suggests that in areas at high risk for malaria, such as Limpopo, management plans should consider not only local climate patterns but those of neighbouring countries as well. These findings highlight the need to strengthen cross-border control of malaria to minimize its spread.

Population based cohort study for pediatric infectious diseases research in Vietnam.

A population-based cohort study on pediatric infectious diseases was established at Khanh Hoa Province, central Vietnam in 2006, to determine the etiology and risk factors for severe pediatric infectious diseases (SPID) such as acute respiratory infection (ARI), diarrhea and dengue which are the major causes of under 5 mortality. A population census survey was conducted in Nha-Trang and Ninh-Hoa to collect demographic, social-behavioral data and disease burden on SPID. The study site covered a population of 353,525 residing in 75,826 households with 24,781 children less than 5 years. Hospital databases from two hospitals covering the region were obtained. Linking the census and hospital databases, we were able to investigate on a variety of SPID such as environmental tobacco smoking exposure and increased risked of pediatric pneumonia hospitalization, population density, water supply and risk of dengue fever and animal livestock and risk of hospitalized diarrhea. To determine incidence, viral etiology and risk factors for pediatric ARI/pneumonia, we setup a population based prospective hospitalized Pediatric ARI surveillance at Khanh Hoa General Hospital, Nha-Trang in February 2007. The study has revealed RSV, rhinovirus and influenza A as major viral pathogens, role of multiple viral infection and its interaction with bacteria in the development of pneumonia. In addition, we are also conducting a birth cohort study to investigate the incidence of congenital infection and its impact on physical-neurological development, and role of host genetic polymorphism on SPID hospitalization in Vietnam. Population mobility, high cost of regular census update and low mortality are the challenges.

Possible association between recent migration and hospitalisation for dengue in an urban population: a prospective case-control study in northern Vietnam.

A prospective case-control study was conducted in urban districts in Hanoi, northern Vietnam to evaluate the effect of migration on the risk of hospitalisation for dengue in a Vietnamese urban population. We enrolled laboratory-confirmed dengue patients aged ≥ 18 years who were hospitalised in local hospitals in November and December 2010. Four neighbourhood-matched controls for each case were recruited within a week of hospitalisation. Sociodemographic data were collected by interviews, and the number of immature and adult mosquitoes within household premises was counted by entomological survey. Matched-pair analyses were conducted using conditional logistic regression models. Among 43 cases and 168 controls, 84% and 83% were migrants from rural areas, respectively. Although statistical significance was marginal, recent migration (residing in study area for ≤ 5 years) independently increased the risk of hospitalisation for dengue compared with inhabitants after controlling for potential confounders (adjusted odds ratio [aOR] = 3.78; 95% confidence interval [CI] = 0.99-14.27), whereas longer-term migration (residing in study area for ≥ 6 years) did not change the risk (aOR = 1.1; 95% CI = 0.30-4.05). Younger age (18-34 years) (aOR = 7.26; 95% CI = 2.39-22.06) and higher adult Aedes aegypti infestation level within household premises (aOR = 9.25; 95% CI = 1.68-51.09) were also independently associated with hospitalisation for dengue. Recent migration from rural areas seems to increase the risk of hospitalisation for dengue in urban populations in endemic areas. Further research including cohort study should be done to confirm the impact of migration on the risk of dengue in urban areas.

Field trial on a novel control method for the dengue vector, Aedes aegypti by the systematic use of Olyset® Net and pyriproxyfen in Southern Vietnam.

BACKGROUND: Jars, tanks, and drums provide favorable rearing/breeding sites for Aedes aegypti in Vietnam. However, the use of insecticides to control mosquitoes at such breeding sites has not been approved in Vietnam since they are also often sources of drinking water, making larval vector control difficult. Mosquito nets pre-treated with long-lasting insecticide treated nets (LLITNs) form an effective measure for malaria control. We examined changes in the abundance of immature Aedes aegypti to evaluate the efficacy of covering ceramic jars with lids comprising one type of LLITN, Olyset® Net, in inhibiting oviposition by adult females, and to evaluate the effect of treating other breeding containers, such as flower vases, inside and around the outside of houses with a slow-release pyriproxyfen formulation to kill pupae. METHODS: We selected 313 households for the trial and 363 households for the control in Tan Chanh, Long An province, Vietnam. In the trial area, Olyset® Net lids were used to cover five major types of water container (ceramic jars, cylindrical concrete tanks, other concrete tanks, plastic drums, and plastic buckets), while pyriproxyfen was used to treat flower vases and ant traps. We also monitored dengue virus transmission by measuring anti-dengue IgM and IgG levels in healthy residents in both control and trial areas to estimate the effectiveness of Olyset® Net at controlling the dengue vector, Aedes aegypti. RESULTS: The container-index and house-index for immature Ae. aegypti fell steeply one month after treatment in the trial area. Lids with Olyset® Net that fit container openings clearly seemed to reduce the presence of immature Ae. aegypti as the density of pupae decreased 1 month after treatment in the trial area. Pyriproxyfen was also effective at killing pupae in the water containers in the trial area. Although the dengue seroconversion rate was not influenced by Olyset® Net, it was lower in two-five year old children when compared to older children and adults in both control and trial areas. CONCLUSIONS: Our study showed that the treatment by Olyset® Net and pyriproxyfen had a strong negative effect on the prevalence of immature Ae. aegypti, which persisted for at least 5 months after treatment.

Effect of housing factors on infestation by Aedes aegypti (L.) and Aedes albopictus Skuse in urban Hanoi City, Vietnam.

To determine the effect of housing factors on infestation with Aedes aegypti (L.) and Aedes albopictus Skuse we conducted an entomological survey and inspection of 267 urban houses in Hanoi City, Vietnam. Two hundred ten pupae and 194 adult Ae. aegypti were collected from 19 and 88 houses, respectively. One hundred eighty-one pupae and 24 adult Ae. albopictus were collected from 21 and 14 houses, respectively. The presence of a private well was associated with increasing infestation with Ae. aegypti adults (p = 0.01) and increased the risk of Ae. aegypti and Ae. albopictus pupal presence (p = 0.04 for Ae. aegypti, p = 0.03 for Ae. albopictus). The presence of an outdoor space in the household premises was associated with a higher risk of Ae. albopictus pupal presence (p = 0.004) and a higher risk of high levels of Ae. albopictus adults (p = 0.01); however, it had no association with infestation with Ae. aegypti. The presence of an air-conditioning unit (p = 0.03) and four or more rooms in the residence (p = 0.02) were negatively and positively associated with the risk for Ae. albopictus presence, respectively.

Population density, water supply, and the risk of dengue fever in Vietnam: cohort study and spatial analysis.

BACKGROUND: Aedes aegypti, the major vector of dengue viruses, often breeds in water storage containers used by households without tap water supply, and occurs in high numbers even in dense urban areas. We analysed the interaction between human population density and lack of tap water as a cause of dengue fever outbreaks with the aim of identifying geographic areas at highest risk. METHODS AND FINDINGS: We conducted an individual-level cohort study in a population of 75,000 geo-referenced households in Vietnam over the course of two epidemics, on the basis of dengue hospital admissions (n = 3,013). We applied space-time scan statistics and mathematical models to confirm the findings. We identified a surprisingly narrow range of critical human population densities between around 3,000 to 7,000 people/km² prone to dengue outbreaks. In the study area, this population density was typical of villages and some peri-urban areas. Scan statistics showed that areas with a high population density or adequate water supply did not experience severe outbreaks. The risk of dengue was higher in rural than in urban areas, largely explained by lack of piped water supply, and in human population densities more often falling within the critical range. Mathematical modeling suggests that simple assumptions regarding area-level vector/host ratios may explain the occurrence of outbreaks. CONCLUSIONS: Rural areas may contribute at least as much to the dissemination of dengue fever as cities. Improving water supply and vector control in areas with a human population density critical for dengue transmission could increase the efficiency of control efforts. Please see later in the article for the Editors' Summary.

The efficacy and physical condition of olyset insecticide-treated nets after 5 years use in rural Lao PDR.

We assessed the insecticidal efficacy of Olyset nets after 5 years of use in rural villages of Lao PDR and evaluated the relationship between the physical condition of the nets and their insecticidal effect. Our results showed that most of the Olyset nets remained effective after 5 years of use; however, there was no significant relationship between the physical condition of the nets (ie, presence of holes, level of stains) and the insecticidal effect. The presence of large holes in polyester nets compared to the Olyset nets suggest the Olyset nets are stronger; however, nearly half of Olyset nets had small holes or had been previously repaired. Interestingly, the insecticide concentration and knockdown (KD) rate for 3 stored nets was low compared to the other nets routinely used in the house. To maintain the effectiveness of Olyset nets in rural villages of Lao PDR and other areas, residents should be advised to repair and store the nets appropriately and avoid exposure to high temperatures and direct sunlight for long periods.

Use of verbal autopsy to determine mortality patterns in an urban slum in Kolkata, India.

OBJECTIVE: To define mortality patterns in an urban slum in Kolkata, India, in the context of a cholera and typhoid fever project. METHODS: In a well-defined population that was under surveillance for 18 months, we followed a dynamic cohort of 63 788 residents whose households were visited monthly by community health workers to identify deaths. Trained physicians performed verbal autopsies and experienced senior physicians assigned the primary cause of death according to the International classification of diseases, 10th edition. We tabulated causes of death in accordance with Global Burden of Disease 2000 categories and assessed overall and cause-specific mortality rates per age group and gender. FINDINGS: During 87 921 person-years of follow-up, we recorded 544 deaths. This gave an overall mortality rate of 6.2 per 1000 person-years. We assigned a cause to 89% (482/544) of the deaths. The leading causes of death, in descending order, were cardiovascular diseases (especially among adults aged over 40 years), cancer, respiratory ailments and digestive disorders. Most deaths in children under 5 years of age were caused by tuberculosis, respiratory infections and diarrhoeal diseases. CONCLUSION: Although the most common causes of death in children were infectious, non-communicable diseases were predominant among adults. There is a need for continuing interventions against infectious diseases in addition to new and innovative strategies to combat non-infectious conditions.

Can daytime use of bed nets not treated with insecticide reduce the risk of dengue hemorrhagic fever among children in Vietnam?

The purpose of this study was to investigate the prevalence of bed net use and elucidate the effect of daytime bed net use on preventing dengue hemorrhagic fever (DHF) among children in Vietnam. We conducted a population-based cross-sectional survey and a matched case-control study in Khanh Hoa Province where not only some pre-schoolchildren but also some school children, who take a nap during lunch break prior to returning to school, used bed nets during the day. Among 36,901 children 2-10 years of age, most used untreated bed nets during the night (98.3%) compared with 8.4% during the day. The results of the case-control study, which defined 151 cases who were hospitalized with DHF in the provincial hospitals and 604 age-matched neighborhood controls, did not support our hypothesis that children using untreated bed nets during the day are less likely to be hospitalized with DHF (adjusted odds ratio = 0.56, 95% confidence interval = 0.23-1.39).

Effect of water supply system installation on distribution of water storage containers and abundance of Aedes aegypti immatures in urban premises of Ho Chi Minh City, Viet Nam.

To assess the effect of installation of a water supply system on the distribution of water storage containers and abundance of Aedes aegypti immatures, we conducted two successive entomological surveys in October 2007 and July 2008 in an urban neighbourhood of Ho Chi Minh City, Viet Nam. In all, 850 water-holding containers, including plastic buckets, water jars, concrete basins, flower vases, ant-traps, outdoor discards, used tyres and plant saucers were observed in 122 premises. Of these, 44 premises already had a water supply system installed at the time of the first survey (i.e. control premises). In the remaining 78 premises, a water supply system was installed 3–6 months before the second survey (i.e. intervention premises). There was a drastic reduction in the number of water storage containers, except concrete basins, between the first and second surveys. We also observed that the distribution of water storage containers in the control and intervention premises was similar. This was probably because the construction of a water supply system before the second survey increased the reliability of the system not only for the residents in intervention premises but also in the control premises (i.e. increased water pressure in the water supply system). The number of plastic buckets and water jars was reduced in the second survey; however, these containers were still an important source of Ae. aegypti pupae. For effective control of dengue infection, it is necessary to conduct entomological monitoring considering the seasonal changes in vector abundance and dengue transmission threshold after installing a water supply system

Effect of peridomestic environments on repeated infestation by preadult Aedes aegypti in urban premises in Nha Trang City, Vietnam.

To determine the effect of peridomestic environments on Aedes aegypti infestation in urban premises, we conducted two consecutive surveys in the hot-dry and cool-wet seasons. Most Ae. aegypti pupae (79%) were recovered from premises where preadult forms (larvae and/or pupae) had been detected in both surveys. Hence, repeated infestation appears to be a useful parameter to identify premises associated with a high potential risk of dengue transmission. Multivariate analysis revealed that not only the persistent presence of containers discarded outdoors, wells, large plastic buckets, jars, and concrete toilet basins in the premises (adjusted odds ratios [aORs] = 63.3, 23.3, 22.5, 6.6, and 5.6, respectively) but also the presence of six or more residents was significantly associated with repeated infestation (aOR = 6.1). Premises with six or more residents along with specific container types from which a large number of pupae were recovered should be targeted in dengue-control programs.

High potential risk of dengue transmission during the hot-dry season in Nha Trang City, Vietnam.

We visited houses and inspected water-holding containers to determine the potential risks of dengue transmission during different seasons. This survey was conducted in two neighbourhoods of Nha Trang City in July and December 2006, which correspond to the middle of the hot-dry season and the beginning of the cool-wet season, respectively. We inspected a total of 1438 wet containers in 196 premises during both survey periods; 20% of the containers were positive for Aedes aegypti larvae and 8% for A. aegypti pupae. Indoor water-holding containers, which were sparsely distributed, exhibited high pupal productivity and efficiency (pupal productivity of a type of container/prevalence of that type of container) in either the first survey conducted in July, or the second, conducted in December. Although rainfall may not influence the number and distribution of water-holding containers in the city, the high average temperature in the first survey period resulted in a higher potential risk of dengue transmission. Our analysis suggests that if intensive source reduction is conducted in summer and containers with high pupal productivity and efficiency are targeted, the risk of dengue transmission in the city could be effectively reduced.

Effect of existing practices on reducing Aedes aegypti pre-adults in key breeding containers in Ho Chi Minh City, Vietnam.

This study aimed to evaluate the effects of existing practices of residents in reducing pre-adult Aedes aegypti (L.) infestation and to assess the effect of dengue-related knowledge on the practices. A house-to-house survey was conducted in two areas with different socioeconomic status in Ho Chi Minh City between October and November 2007. Some residents in both the areas used covers on the productive containers such as the jars and plastic buckets (i.e., 58% and 81% in the two study areas), and it was effective in reducing Ae. aegypti infestation: odds ratio (OR) of 4.0 and 4.9 (95% confidence interval [CI]: 1.49-10.76 and 1.2-19.57, respectively) for the containers with inappropriate covers compared with those with appropriate covers in the two areas, respectively. Appropriate cover use was an effective practice; however, no beneficial role of the knowledge related to dengue in promoting the practice was identified.

[Evaluation on the safety of a group A + C meningococcal polysaccharide vaccine].

OBJECTIVE: To evaluate the safety of a group A + C meningococcal polysaccharide vaccine as part of a phase IV clinical trial. METHODS: The study area was divided into 108 clusters according to the principle of cluster randomization, stratified and paired sampling methods. 54 out of 108 clusters served as observation groups were administered A + C vaccine, while the rest 54 groups were administered Vi polysaccharide vaccine. An adverse event surveillance system was established to monitor the adverse events following the vaccination campaign. Identical form and methods were used for data collection to investigate the adverse events following the vaccination of both A+ C vaccine and Vi vaccine. RESULTS: 34,543 people were vaccinated, including 18,167 of whom received A + C vaccine, while the other 16,376 received Vi vaccine. The rates of immediate injection reaction and unsolicited non-serious adverse events from A + C vaccine group were 0.44% and 0.38% while of Vi vaccine group were 0.79% and 0.73% respectively. At the solicited adverse event survey on 3-day-post-vaccination, 1239 vaccinees were followed-up including 771 received A + C vaccine and 468 received Vi vaccine. The local injection reaction rate of A + C vaccine group on the 1st day was significantly higher (X2 = 13.98, P = 0.0002) than that of Vi vaccine group. Neither the local injection reaction rate nor the system reaction rate between both groups was significantly different on 2nd and 3rd day, post vaccination. It was not statistically different when comparing fever onset rate between those who received vaccine and those who did not, in each vaccine group. There were no serious adverse events observed. CONCLUSION: Results showed that the side effects of A + C vaccine and the Vi vaccine were mild and safe for vaccination campaigns targeting on populations at different age.

The malaria and typhoid fever burden in the slums of Kolkata, India: data from a prospective community-based study.

Recent research has indicated that the malaria burden in Asia may have been vastly underestimated. We conducted a prospective community-based study in an impoverished urban site in Kolkata, India, to estimate the burden of malaria and typhoid fever and to identify risk factors for these diseases. In a population of 60452 people, 3605 fever episodes were detected over a 12-month period. The blood films of 93 febrile patients contained Plasmodium (90 P. vivax, 2 P. falciparum and 1 P. malariae). Blood cultures from 95 patients grew Salmonella enterica serotype Typhi. Malaria patients were found to be significantly older (mean age 29 years) compared with patients with typhoid fever (15 years; P<0.001) but had similar clinical features on presentation. Having a household member with malaria, illiteracy, low household income and living in a structure not built of bricks were associated with an increased risk for malaria. Having a household member with typhoid fever and poor hygiene were associated with typhoid fever. A geographic analysis of the spatial distribution of malaria and typhoid fever cases detected high-risk neighbourhoods for each disease. Focal interventions to minimise human-vector contact and improved personal hygiene and targeted vaccination campaigns could help to prevent malaria and typhoid fever in this site.

Mark-release-recapture experiments with Anopheles saperoi (Diptera: Culicidae) in the Yona Forest, northern Okinawa, Japan.

Six mark-release-recapture experiments with Anopheles saperoi Bohart and Ingram were performed in the Yona Forest, northern Okinawa, Japan from June 1998 - November 1999, in order to estimate the gonotrophic cycle, survival, spatial distribution, flight range, and population size of An. saperoi. Adults and immature An. saperoi were collected from the Yona Forest area, taken to the laboratory and maintained under a controlled temperature and humidity in order to get a lager number of mosquitos for the mark-release-recapture experiments. Cohorts of An. saperoi females and males, numbering 3,016, 4,728, 327, and 2,603 for experiments I, II, III, and IV, respectively, were released. Cohorts of An. saperoi females only, numbering 709 and 586 for experiments V and VI, respectively, were also released. At the release site, the An. saperoi were marked with 0.5% fluorescent dye Rhodamine B and released. The recapture rates were 14 (0.93%), 33 (1.40%), 3 (1.83%), 32 (2.46%), 14 (1.97%), and 22 (3.75%) for experiments 1, II, III, IV, V, and VI, respectively. The length of the gonotrophic cycle of the recaptured An. saperoi females was estimated to be about 4 days, through the dissection method. The daily survival rate was estimated to be 0.73 by regression coefficient. The spatial distribution of marked, recaptured An. saperoi was similar to that of unmarked captured An. saperoi. The spatial distribution of the marked, recaptured An. saperoi among the collection site categories was significantly different. The observed differences in the frequency distribution of marked recaptured An. saperoi were considered to be due to the spatial variation of the habitats between the collection sites. The maximum flight range of the recaptured An. saperoi recorded in this study was 0.93 km. The population size of An. saperoi females in the study area was estimated by the Seber method to be 23,841, 1,182, 3,514, 5,679, and 9,238 for experiments I, II, IV, V, and VI, respectively. The estimated population size has a low standard of error using the Seber method, therefore we estimated our population size reasonably well. The population attributes and ecology of An. saperoi in the Yona Forest, in northern Okinawa are discussed.

Susceptibility of the mosquitoes Anopheles minimus, An. sinensis, and An. saperoi (Diptera: Culicidae) from the Ryukyu Archipelago, Japan, to the rodent malaria Plasmodium yoelii nigeriense.

The susceptibility of three anopheline mosquitoes, Anopheles minimus Theobald, An. sinensis Wiedemann, and An. saperoi Bohart & Ingram, from the Ryukyu Archipelago to the rodent malaria, Plasmodium yoelii nigeriense was examined to find new vectors other than An. stephensi Liston for rodent malaria studies in the laboratory. The survival rate of the mosquitoes after feeding on mice infected with P. y. nigeriense was also examined. The Beech strain of An. stephensi from India was compared with An. minimus from Ishigaki Island, and An. sinensis and An. saperoi from Okinawa Island. Oocysts were first found on day 3 after feeding on mice infected with P. y. nigeriense in An. stephensi, on day 4 in An. minimus and An. saperoi, and day 6 in An. sinensis. From 8 to 14 d after feeding on malaria-positive mice, oocysts were present in 97.2-100% of An. stephensi, 85.7-100% of An. saperoi, 20-74.1% of An. minimus, and 12.5-13.3% of An. sinensis. The duration of oocyst occurrence in An. saperoi was 55 d, the longest among the anopheline mosquitoes used in this study. On day 8 after feeding, sporozoites were found in the salivary glands and heads of all the mosquitoes tested. From the 10th to 16th d, sporozoites were present in the salivary glands of 14.9% (range, 9.1-28.0%) of An. minimus, 47.3% (40.7-58.1) of An. saperoi, and 96.2% (94.1-97.2) of An. stephensi, but were absent in An. sinensis. Anopheles saperoi could be an excellent vector of P. y. nigeriense because it has comparatively high susceptibility and high longevity even after feeding on infected mice.