Trends in asthma visits to accident and emergency centres in Trinidad during 1997 and associations with climate variables

OBJECTIVES: To describe trends in asthma visits to Accident and Emergency (A&E) facilities during 1997 and to examine their associations with climatic conditions. DESIGN AND METHODS: A census of patients with asthma, defined as those who required brochodilator nebulization, was taken at five A&E facilities in Trinidad. Data on patients' age, gender and date of visit were obtained from the A&E records and, climate variables, including rainfall, temperature, relative humidity, and wind speed, were obtained from the Meteorological Office. RESULTS: There was a total of 27,848 asthma visits to the five facilities during 1997, of which the paediatric population(<16 years) accounted for 43 percent. There were steady increases in adult and elderly visits from January to December. A sharp increase in paediatric visits was observed in September, which coincided with the start of the school year. The results of multiple regression analysis indicated that paediatric visits to the A&E were positively associated with temperature and wind speed, while adults' visits were positively associated with temperature and relative humidity. None of the climatic variables predicted asthma visits in the elderly. CONCLUSION: There is a need for further research to explain the increase in paediatric visits at the start of the school year as well as to elucidate the mechanism for the observed associations between climate and asthma visits. (Au)

Weather as a predictor of the frequency of asthmatic attacks in Barbados - abstract

Daily data on asthmatic patients seen in the Accident and Emergency Department of the Queen Elizabeth Hospital for the years 1983 and 1989-1991, and corresponding daily data for the meterological variables of wind speed, relative humidity (0800 hr), vapour pressure and minimum and maximum temperatures were analysed to determine the statistical relationships that might exist. The results show positive correlation between asthma attacks and relative humidity and vapour pressure, and negative correlations for the wind speed. The data also show the existence of a seasonal variation in asthmatic attacks. It is suggested that this variation is due to the transport of aero-allergens into Barbados through the trade winds (AU)

Laboratory colonization and maintenance of Toxorhynchites moctezuma

A colony of Toxorhynchites moctezuma was established at the Caribbean Epidemiology Centre in Trinidad in 1984. Toxorhynchites moctezuma was maintained in cages with high humidities. Eggs were deposited most frequently in a cut bicycle tire containing water. A minimum of 42 h was required for hatching, but 94 percent hatched between 43 and 51 h. Aedes aegypti larvae were supplied as prey. Larval development times varied with the quantity of prey offered, but when fed ad lib, peak developmental time was 18 days. Mean pupal developmental time was 5.5 days. Although only 12 percent of larvae survived to pupation in 3 years of production, our experience indicates this species would be a likely candidate for mass production and release.(AU)

Incidence and diel pattern of oviposition outdoors of the mosquito Aedes aegypti (L.) (Diptera: Culicidae) in Trinidad W. I. in relation to solar aspect

The incidence and diel patterns of oviposition of domestic Aedes aegypti in Trinidad, West Indies during the middle of the wet season (July and August) was compared, using modified ovitraps, in unshaded peridomestic outdoor sites facing east or west. Sites close to each other along a transect differed greatly in the total eggs they received, 18.2 percent of sites receiving 50.6 percent of the eggs. Sites receiving most eggs were close to other breeding sites. The incidence of oviposition in sites facing west, as measured by the number of eggs laid (>59 percent) and by the number of occurrences of eggs (>57 percent), was greater than in sites facing east. The diel pattern of oviposition was closely similar in sites facing east and west, indicating that the sun's azimuth at the moment of oviposition does not determine whether a female lays in sites facing east or west. The diel pattern of oviposition resembled an earlier study in being bimodal but differed from it in featuring a much larger morning peak (comprising more than 34 percent of eggs laid v. about 5 percent in the earlier study). This bimodal pattern closely resembles, the diel periodicity of landing on humans described previously by several authors and is probably close to the typical oviposition pattern for Ae. aegypti; an artefact may have modified the oviposition periodicity characterized earlier. In the evening significantly more eggs were laid facing east. These findings have implications for effective placement of ovitraps for surveillance or suppression of Ae. aegypti, and give rise to an hypothesis which invokes responses to microclimate to account for the form of the bimodal oviposition pattern (AU)

Observations on the seasonal incidence and diel oviposition periodicity of haemagogus mosquitoes (Diptera: Culicidae) in Trinidad, W.I.: part I

The diel oviposition periodicity of sylvan Haemagogus janthinomys Dyar in the Pt. Gourde Forest, Trinidad, West Indies was monitored weekly for 53 weeks using conventional ovitraps. During the wet season (September to November 1981 and May to September 1982) a large well-defined unimodal peak occurred six to eight hours after sunrise (comprising 94 percent of eggs laid and 91 percent occurrences). During the dry season (December 1981 to May 1982), a small less-well-defined peak occurred two to four hours before sunset (comprising 6 percent of eggs laid). The combined data showed a diurnal oviposition pattern with eggs laid from noon to sunset. The numbers of eggs and of used ovitraps found during the wet season were significantly (P<0.001) higher than those found during the dry season.(AU)

ELISA for Schistosoma mansoni infection: durability of blood spots on filter paper

We investigated the persistence of seropositivity for Schistosoma mansoni infection by ELISA in blood spots on filter paper strips stored for up to 16 weeks under conditions ranging from "tropical" temperatures and humidity to storage at -20 degrees Centigrade. High humidity (60 to 85 percent RH) appeared to cause greater deterioration of samples than high temperatures. Storage in a dessicator at 30 degrees Centigrade was as effective as storage in a freezer at -20 degrees Centigrade (Summary)

Water content level in inspired air on specific airway resistence in rats

The effect of increasing water content in inspired air on specific airway resistence in rats was assessed. The results show that specific airway resistances were significantly related to the water content of the inspired air, above 15.02 mg/m3, the duration of water content exposure and to the type of water nebulized. It is suggested that the increase is composed of a local and neural element caused by accumulation of mucus or mucosal swelling and changes in the composition and consistency of the mucus lining layer, respectively (AU)

Factors contributing to increased airway resistance with over humidification of inspired air - abstract

Inhalation of air containing increased water content has been shown to cause increased specific airway resistance (sRaw). It has been postulated that these changes might be related to reflex broncho-constriction and/or mucosal swelling. We attempted to elucidate the exact mechanism of action by a series of studies in rats, designed to demonstrate whether changes in specific airway resistance (as measured by whole body plethysmography), due to inhalation of air saturated with distilled water or tap water were preventable or reversible by either sympathomimetic (adrenaline), parasympatholytic (atropine) or mucolytic (N-acetyl cysteine) drugs. The results obtained showed that inhalation of air containing either tap or distilled water above the "safe level" (15.02gm/m(to the 3rd power) of humidification caused a significant increase in specific airway resistance above the control (p<0.01), with a slightly greater increase with tap water. Administration of adrenaline in aerosol to inspired air containing distilled or tap water vapour for six minutes caused no significant change in sRaw. A significant decrease in sRaw was obtained by injecting intramuscularly atropine (p0.01): and administration of N-acetylcysteine with inspired air containing distilled or tap water vapour caused an increase in sRaw above inhalation containing only tap or distilled water vapour, (p<0.05) which decreased with suction (p<0.05). Likewise N-acetyl cystine with distilled water or tap water vapour caused a significant increase in sRaw above that of inspired air with tap or distilled water alone (p<0.05) which significantly decreased with administration of atropine. These results suggest that mucosal swelling, reversible by parasympatholytic therapy, is a major factor in the increased specific airway resistance with over humidification of inspired air. There is no convincing evidence that broncho-constriction is of major importance. Mucolytic agents may aid in decomposing mucus but their effect on sRaw appears to be negative unless the decomposed products are moved by coughing or suction, and may be dangerous in patients who have no cough reflex (AU)

Variation in forced expiratory volume curves of asthmatic patients with increased water content

An experiment was designed to provide information on the "safe" level of humidifiction of inspired air in asthmatic patients. It was found that air at 25 degrees celcius and 70 percent relative humidity (RH) (16.11 gm/cu m WC) and 35 degrees celcius, 40 percent RH (17.80 gm/cu m) had no significant effect on forced expiratiory volume parameters. At 25 degrees celcius, 95 percent RH (21.88 gm/cu m WC) and above changes in VC/PVC, FEV 1 and FEV 3, MMF and MBC were significantly affected (P < 0.01). Approximately 21.88 gm/cu m Water content is considered the point at which humidification of inspired air ceases to be therapeutically useful.(AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. I. Description of the study area

Bush Bush Island and the surrounding Nariva Swamp, eastern Trinidad, are described in terms of their topography, flora, and fauna as an introduction to a series of papers reporting the results of 5 years of arbovirus studies in this area. (AU)