A new strategy for treating nets. Part 2: users' perceptions of efficacy and washing practices and their implications for insecticide dosage.

The conventional way to treat a mosquito net with pyrethroid insecticide is to apply a standard dosage every 6-12 months, and to avoid washing the net until just before retreatment. In some places, nets are normally washed much more often than this, and it may then be more appropriate to apply smaller amounts of insecticide after each wash. The choice of strategy must take into account not only biological effectiveness, but also users' perceptions of this effectiveness and their net-washing habits. We used focus groups to compare users' responses to nets treated with different dosages and chemicals. One hundred current net users in urban Dares-Salaam were each given a net that had been pretreated either with permethrin (200 or 500 mg/m2), or with lambdacyhalothrin (3 or 15 mg/m2), or with water. Neither participants nor investigators knew which group had received which treatment. Focus group discussions were held after 2, 8 and 12 weeks. Participants greatly preferred treated nets. Low doses were perceived to be less effective, especially after 8 and 12 weeks. After 12 weeks most participants had washed their nets, despite requests to the contrary Dirty nets were regarded as unhealthy and socially unacceptable. Few participants experienced side-effects or expressed fears about the safety of treatment. We conclude that asking people to refrain from washing their nets is unrealistic. A 'low-dose frequent-treatment' strategy of insecticide application may be more appropriate in the long run. At first, however, low doses give perceptibly inferior protection. An initial high (loading) dose, followed by frequent lower (maintenance) dosages, might solve this problem.

Exercise-induced bronchoconstriction by ethnicity and presence of asthma in British nine year olds.

BACKGROUND: The prevalence of exercise-induced bronchoconstriction among British children by ethnicity has not been studied. METHODS: Peak expiratory flow rate (PEFR) was measured before and after an exercise challenge test using a cycle ergometer in 593 nine year olds from Scottish and inner city English schools. Logistic regression analysis was carried out to assess the association between changes in PEFR with exercise by reported asthma, ethnicity, and sex. RESULTS: The probability of exercise-induced bronchoconstriction was greater among the asthmatics than in either the children without asthma attacks or wheeze, or in the children with only wheeze (p < 0.01). Asian children were 3.6 times more likely to have exercise-induced bronchoconstriction than white inner city children, and also were more likely to have exercise-induced bronchoconstriction than those from the other ethnic groups (p < 0.01). CONCLUSION: Exercise challenge can assess the prevalence of asthma in the community and detect under-reporting of asthma in ethnic minorities.

Response surface model of the effect of pH, sodium chloride and sodium nitrite on growth of Yersinia enterocolitica at low temperatures.

A fractional factorial design was used to measure the effects and interactions of temperature (5, 12, 19 degrees C), pH (4.5-8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 micrograms/ml) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting plate count data to the Gompertz equation. Quadratic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generation times were obtained using response surface analysis. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These models provide a means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.

Adiposity in aboriginal people from Arnhem Land, Australia: variation in degree and distribution associated with age, sex and lifestyle.

A number of researchers have found substantial sex, population and group differences in adiposity and fat-distribution patterns, but there is relatively little information on body fat distribution in Aboriginal groups, especially for the indigenous people of Australia. This study, the largest of its kind for Australian Aboriginal people, presents information on adiposity and fat distribution in 425 Yolngu, a group of Aboriginal people living in a number of communities representing a wide range of lifestyles, in northeast Arnhem Land, Australia. Using BMI standards developed for people of European descent, the majority of the individuals in this study were lean, and the incidence of obesity was considerably less than in other Australian groups, Aboriginal and non-Aboriginal. For the Yolngu in this study the relationship between ageing and adiposity is similar to that reported for tradition-orientated Aboriginal people, as well as for a number of other indigenous groups, viz., while the men maintain their weight into old age, the women, once they are past early adulthood, lose body fat with age. The results from the present study suggest that the age at which the Yolngu women start to gain, and subsequently lose, body fat is associated with differences in degree of acculturation. As has been found in other populations, age- and sex-related differences in body fat distribution occur, but no correlation was found between adiposity and fat distribution. The Aboriginal women and men, however, had a significantly more central distribution of subcutaneous fat than their non-Aboriginal counterparts. Our findings have implications for the health and demography of Aboriginal people in general, and the Yolngu in particular, as they continue the transition from hunting and foraging towards a more 'westernized' lifestyle.

A Procedure for the Direct Microscopic Count of Bacteria in Non-fat Dry Milk.

Bacteria in non-fat dried milk (NDM) were enumerated by a method involving preliminary solubilization of the milk proteins in 0.015 N NaOH followed by centrifuging, washing in the NaOH, and microscopically examining stained smears. The method was used to enumerate bacteria in samples of NDM obtained from government surplus stocks or from local retail sources. Bacterial counts from surplus NDM ranged from 4.64 × 105 to 2.83 × 106/g (the mean and median were, respectively, 6.23 and 2.84 × 106/g). Counts from retail samples ranged from 4.48 × 105 to 2.42 × 107/g (mean and median were 5.57 and 2.85 × 106/g). The predominant bacteria in some samples were paired streptococci; other samples contained rod-shaped bacteria, some with identifiable spores. Comparison of this method with the Levowitz-Weber method indicated that it produced fewer artifacts, was applicable to NDM samples containing a wider range of bacteria, and did not require the use of the potentially carcinogenic tetrachloroethane.