Joint modelling compared with two stage methods for analysing longitudinal data and prospective outcomes: A simulation study of childhood growth and BP.

There is a growing debate with regards to the appropriate methods of analysis of growth trajectories and their association with prospective dependent outcomes. Using the example of childhood growth and adult BP, we conducted an extensive simulation study to explore four two-stage and two joint modelling methods, and compared their bias and coverage in estimation of the (unconditional) association between birth length and later BP, and the association between growth rate and later BP (conditional on birth length). We show that the two-stage method of using multilevel models to estimate growth parameters and relating these to outcome gives unbiased estimates of the conditional associations between growth and outcome. Using simulations, we demonstrate that the simple methods resulted in bias in the presence of measurement error, as did the two-stage multilevel method when looking at the total (unconditional) association of birth length with outcome. The two joint modelling methods gave unbiased results, but using the re-inflated residuals led to undercoverage of the confidence intervals. We conclude that either joint modelling or the simpler two-stage multilevel approach can be used to estimate conditional associations between growth and later outcomes, but that only joint modelling is unbiased with nominal coverage for unconditional associations.

Effect of Water Activity and Packaging Material on the Quality of Dehydrated Taro (Colocasia esculenta (L.) Schott) Slices during Accelerated Storage.

The quality of dehydrated taro slices in accelerated storage (45°C and 75% RH) was determined as a function of initial water activity (aw) and package type. Color, rehydration capacity, thiamin content, and α-tocopherol content were monitored during 34 weeks of storage in polyethylene and foil laminate packaging at initial storage aw of 0.35 to 0.71. Initial aw at or below 0.54 resulted in less browning and higher rehydration capacity, but not in significantly higher α-tocopherol retention. Foil laminate pouches resulted in a higher rehydration capacity and increased thiamin retention compared to polyethylene bags. Type of packaging had no effect on the color of the samples. Product stability was highest when stored in foil laminate pouches at 0.4aw. Sensory panels were held to determine the acceptability of rehydrated taro slices using samples representative of the taro used in the analytical tests. A hedonic test on rehydrated taro's acceptability was conducted in Fiji, with panelists rating the product an average of 7.2 ± 1.5 on a discrete 9-point scale. Using a modified Weibull analysis (with 50% probability of product failure), it was determined that the shelf life of dehydrated taro stored at 45°C was 38.3 weeks.

Conditions associated with Clostridium sporogenes growth as a surrogate for Clostridium botulinum in nonthermally processed canned butter.

The objective of this study was to better understand the effect of butter composition and emulsion structure on growth and survival of Clostridium sporogenes, used as a surrogate for C. botulinum in canned butter. The lack of a thermal process step in commercially available canned butter raises questions of potential safety, because it is hermetically sealed and generally exhibits anaerobic growth conditions, which are optimal for Clostridium botulinum growth. Without thermal processing, low-acid canned foods must have inhibitory factors present to prevent C. botulinum growth. Some potential intrinsic inhibitory factors, or hurdles, within butter include: reduced water activity, acidity in cultured products, elevated salt content, and the micro-droplet nature of the aqueous phase in the butter emulsion. It was hypothesized that a normal, intact butter emulsion would have sufficient hurdles to prevent C. botulinum growth, whereas a broken butter emulsion would result in a coalesced aqueous phase that would allow for C. botulinum growth. Batch-churned butter was inoculated with C. sporogenes; butter samples with varying salt contents (0, 0.8, 1.6, and 2.4% wt/wt NaCl) were prepared and stored in coated steel cans for varying times (1 or 2 wk) and temperatures (22 or 41°C) to determine temperature and emulsion structure effects on C. sporogenes growth. Samples stored at 41°C showed a significant increase in C. sporogenes growth compared with those stored at 22°C. Furthermore, NaCl addition was found to have a significant effect on C. sporogenes growth, with 0.8% NaCl promoting more growth than 0%, but with decreases in growth observed at 1.6 and 2.4%. Uninoculated control plates were also found to have bacterial growth; this growth was attributed to other anaerobic bacteria present within the cream. It was concluded that removal of the hurdle created by the micro-droplet size of the emulsion aqueous phase could result in C. botulinum growth even at elevated salt levels and, therefore, home preparation of canned butter is not advisable. It is also possible that commercially canned butter, if heat abused, could potentially allow for C. botulinum growth and, therefore, consumption is not recommended.

Change in mutagenicity in white rice after accelerated and long-term storage.

Certain reactions that occur in food during storage, such as nonenzymatic browning and lipid oxidation, form compounds that have been shown to be mutagenic. It is possible that over long storage periods, significant amounts of these products could be formed. Although some research has been published concerning the mutagenicity of foods due to processing or cooking, little research has been done regarding mutagenicity of foods stored for an extended time. The objective of this research was to determine the potential mutagenicity of white rice held in accelerated and long-term storage using the Ames Salmonella/microsome assay. Fresh long-grain white rice was packaged in foil laminate pouches and held at 60 degrees C for 18 wk. Rice stored for > 25 y in an oxygen-free environment at or below room temperature in size number 10 cans was obtained from residential storage. The standard plate-incorporation method was used to evaluate the mutagenic potential of all treatments using Salmonella typhimurium tester strains TA97a, TA98, TA100, and TA102. Samples were plated at 5 dilutions with and without rat liver S9 enzyme. A solvent control was also plated for each strain. Treatments yielding counts at least double the solvent control level were considered mutagenic. Plate counts for all treatments fell well below the required doubling of the solvent control value. White rice held in accelerated and long-term storage appears not to increase in mutagenic compounds as measured by the Ames assay, supporting its use for long-term storage purposes such as emergency preparedness and humanitarian food aid.

Cooling rate effect on outgrowth of Clostridium perfringens in cooked, ready-to-eat turkey breast roasts.

The potential for Clostridium perfringens spores to germinate and grow in cooked, ready-to-eat turkey products was evaluated to determine a safe cooling rate within the critical temperatures of 48.9 C (120 F) through 12.8 C (55 F). Raw turkey deli breast roasts were inoculated with a cocktail of C. perfringens spores (NCTC 8238, NCTC 8239, and NCTC 10388) and cooked in a steam oven to an internal temperature of 72 C. The sample roasts were then cooled through the critical cooling range at rates yielding cooling times of 6, 8, and 10 h. Turkey roasts were analyzed for spore growth and multiplication using tryptose-sulfite-cycloserine agar and anaerobic incubation at 37 C for 48 h. Cooling times of 6 and 8 h showed no proliferation of C. perfringens that would violate the USDA/Food Safety Inspection Service safe cooling standard criteria, which would allow no more than a 1 log10 multiplication between 48.9 and 12.8 C. A 9.6-h cooling period between the designated temperatures at a 95% confidence interval was determined to be adequate for nonproliferation of C. perfringens. On the other hand, a 95% tolerance interval would be more stringent in that it suggests no more than an 8.9-h cooling period. Tolerance intervals required that 95% of all our observations did not exceed the limit of 1 log10 increase in C. perfringens. This study indicated that in cooked, ready-to-eat turkey deli breasts, a cooling period between 48.9 C (120 F) and 12.8 C (55 F) of no greater than 8.9 h should be utilized to prevent possible C. perfringens foodborne outbreaks.

Savings/credit group formation and change in contraception.

We examine the characteristics of women who chose to join a women's savings or credit group organized by Save the Children USA in a rural area of Bangladesh, and the impact of participation on contraceptive use. The data are taken from a panel survey conducted in 1993, shortly before the groups were formed, and in 1995 after interventions began. Our findings show that although demographic and socioeconomic characteristics have only a weak relationship to the decision to join a program, the treatment that a woman receives from her husband is associated with participation. We also find evidence that the credit program tends to attract women who are already using contraception. The analysis of program impact on the use of modern contraceptives reveals a positive effect of the credit program, after we adjust for this selectivity; we see no evidence of an effect of participation in a savings group.

Pulmonary availability of isotretinoin in rats after inhalation of a powder aerosol.

Repeated oral administration of chemopreventive retinoids such as isotretinoin over extended periods of time is associated with intolerable systemic toxicity. Here isotretinoin was formulated as a powder aerosol, and its delivery to the lungs of rats was studied with the aim to explore the possibility of minimizing adverse effects associated with its oral administration. Rats received isotretinoin orally (0.5, 1 or 10 mg kg(-1)) or by inhalation (theoretical dose approximately 1 or approximately 10 mg kg(-1)) in a nose-only inhalation chamber. Isotretinoin was quantitated by high-pressure liquid chromatography in plasma and lung tissue. The ratios of mean area of concentration-vs-time curve (AUC) values in the lungs over mean AUCs in the plasma for isotretinoin following single or repeated aerosol exposure surpassed those determined for the oral route by factors of between two (single low-dose) and five (single high-dose). Similarly, the equivalent ratios for the maximal peak concentrations in lungs and plasma obtained after aerosol exposure consistently exceeded those seen after oral administration, suggesting that lungs were exposed to higher isotretinoin concentrations after aerosol inhalation than after oral administration of similar doses. Repeated high doses of isotretinoin by inhalation resulted in moderate loss of body weight, but microscopic investigation of ten tissues including lung and oesophagus did not detect any significant aerosol-induced damage. The results suggest that administration of isotretinoin via powder aerosol inhalation is probably superior to its application via the oral route in terms of achieving efficacious drug concentrations in the lungs.

The impact of family planning service provision on contraceptive-use dynamics in Morocco.

This article uses linked data from the 1995 Morocco DHS calendar and the 1992 Morocco DHS service-availability module to study the effect of service environment on contraceptive discontinuation, switching, and adoption of a modern method following a birth. The 1995 Morocco DHS also collected information on the source of supply for each episode of use of a modern method recorded in the calendar, allowing study of the association between the source of supply and discontinuation and switching rates. Multilevel event-history models are used to evaluate the impact of individual-level sociodemographic characteristics and community-level indicators of family planning service provision. The findings show that the presence of a nearby public health center is associated with higher modern-method adoption after a birth and lower method-failure rates; the presence of a pharmacy is associated with lower discontinuation due to side effects or health concerns. The degree of method-choice potential has a positive impact on both the rate of switching from the pill to another modern method and on modern-method adoption after a birth.

PIP: This study examined the relationship between the service context and the separate components of contraceptive adoption and continuation in Morocco. Data were obtained on contraceptive adoption and continuation from the 1995 Demographic and Health Survey (DHS) among 4753 women 15-49 years old (3324 were interviewed in 1992) and on the service context from the 1992 DHS Service Availability Module. Four reasons were given for switching or discontinuation. Switching was due to pregnancy, adopting another modern method, adopting a traditional method, or not using any method. Event history analysis (discrete time) findings reveal that the number of methods available significantly increased postpartum adoption and only weakly related to switching from the pill. Women who used a nongovernment source were more likely to discontinue using for method related reasons and to stop using the pill at discontinuation. The availability of public health centers within 5 km increased postpartum method adoption. The availability of pharmacies in the community significantly decreased the risk of discontinuing the pill because of side effects and health concerns. One caveat is that considerable unexplained cluster level variation is likely to be due to service quality measures, which were not available. Estimates could also be biased due to endogeneity of variables.

Contraceptive switching in Bangladesh.

Bangladesh has experienced a substantial decline in fertility that has been achieved by means of a large increase in the use of modern methods of contraception. As contraceptive prevalence increases, aspects of contraceptive-use dynamics, including reasons for discontinuation and behavior after discontinuation, become important influences on fertility. This report uses calendar data from the 1993-94 Bangladesh Demographic and Health Survey to examine contraceptive behavior following discontinuation of modern-method use. The individual-level characteristics found to influence switching behavior include the method used, method-related difficulties with previous contraceptive use, and education. A large amount of unexplained variation in switching rates remains, however, largely at the individual level, but also at the community level for certain types of transition.