Health Care Provider Knowledge and Practices Regarding Folic Acid, United States, 2002–2003

Objective: To assess health care providers (HCP) knowledge and practices regarding folic acid (FA) use for neural tube defect (NTD) prevention. Methods: Two identical surveys were conducted among 611 obstetricians/gynecologists (OB/GYNs) and family/general physicians (FAM/GENs) (2002), and 500 physician assistants (PAs), nurse practitioners (NPs), certified nurse midwives (CNMs), and registered nurses (2003) to ascertain knowledge and practices regarding FA. For analysis, T-tests, univariate and multivariate logistic regression modeling were used. Results: Universally, providers knew that FA prevents birth defects. Over 88% knew when a woman should start taking folic acid for the prevention of NTDs; and over 85% knew FA supplementation beyond what is available in the diet is necessary. However, only half knew that 50% of all pregnancies in the United States are unplanned. Women heard information about multivitamins or FA most often during well woman visits in obstetrical/gynecology (ob/gyn) practice settings (65%), and about 50% of the time during well woman visits in family/general (fam/gen) practice settings and 50% of the time at gynecology visits (both settings). Among all providers, 42% did not know the correct FA dosage (400 μg daily). HCPs taking multivitamins were more than twice as likely to recommend multivitamins to their patients (Odds Ratio [OR] 2.27 95%, Confidence Interval [CI] 1.75–2.94). HCPs with lower income clients (OR 1.49, CI 1.22–1.81) and HCPs with practices having more than 10% minorities (OR 1.46, CI 1.11–1.92) were more likely to recommend supplements. NPs in ob/gyn settings were most likely and FAM/GENs were least likely to recommend supplements (OR 3.06, CL 1.36–6.90 and OR 0.64, CL 0.45–0.90 respectively). Conclusions: Knowledge about birth defects and the necessity of supplemental FA was high. Increasing knowledge about unintended pregnancy rates and correct dosages of FA is needed. The strongest predictor for recommending the use of FA supplements was whether the provider took a multivitamin

Predicting Rift Valley Fever Inter-epidemic Activities and Outbreak Patterns: Insights from a Stochastic Host-Vector Model

<div><p>Rift Valley fever (RVF) outbreaks are recurrent, occurring at irregular intervals of up to 15 years at least in East Africa. Between outbreaks disease inter-epidemic activities exist and occur at low levels and are maintained by female <i>Aedes mcintoshi</i> mosquitoes which transmit the virus to their eggs leading to disease persistence during unfavourable seasons. Here we formulate and analyse a full stochastic host-vector model with two routes of transmission: vertical and horizontal. By applying branching process theory we establish novel relationships between the basic reproduction number, <i>R</i>₀, vertical transmission and the invasion and extinction probabilities. Optimum climatic conditions and presence of mosquitoes have not fully explained the irregular oscillatory behaviour of RVF outbreaks. Using our model without seasonality and applying van Kampen system-size expansion techniques, we provide an analytical expression for the spectrum of stochastic fluctuations, revealing how outbreaks multi-year periodicity varies with the vertical transmission. Our theory predicts complex fluctuations with a dominant period of 1 to 10 years which essentially depends on the efficiency of vertical transmission. Our predictions are then compared to temporal patterns of disease outbreaks in Tanzania, Kenya and South Africa. Our analyses show that interaction between nonlinearity, stochasticity and vertical transmission provides a simple but plausible explanation for the irregular oscillatory nature of RVF outbreaks. Therefore, we argue that while rainfall might be the major determinant for the onset and switch-off of an outbreak, the occurrence of a particular outbreak is also a result of a build up phenomena that is correlated to vertical transmission efficiency.</p></div

The parameters for the RVF model for high rainfall and moderate temperature (wet season) for model in Table 2 with values, range and references.

<p>Note that all parameter units are days. The parameter <i>α</i>₁ is a function of the mosquito’s gonotrophic cycle (the amount of time a mosquito requires to produce eggs) and its preference for livestock blood, while <i>α</i>₂ is a function of the ruminant’s exposed surface area, the efforts it takes to prevent mosquito bites (such as swishing its tail), and any vector control interventions in place to kill mosquitoes encountering cows or prevent bites [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005167#pntd.0005167.ref024" target="_blank">24</a>].</p

Solution of Eq (14) when the product <i>R</i>₁₂ × <i>R</i>₂₁ is greater than unity.

<p>The curves in (a) and (b) are contours in the plane (<i>R</i>₁₂, <i>R</i>₂₁), along which the probabilities of extinction and invasion respectively, after an introduction of a single vector is constant. In (c) and (d) we plot probabilities of extinction and invasion respectively, when varying parameters <i>α</i>₁ and <i>α</i>₂. The values of the remaining parameters in days are as follows: <i>μ</i>₁ = 1/30, <i>μ</i>₂ = 0.00046, <i>β</i>₁₂ = 0.676, <i>β</i>₂₁ = 0.28, <i>ϵ</i>₂ = 0.25, <i>m</i>₀ = 10.</p

Theoretical prediction of the power spectrum density (PSD) (Eq (13)) for fluctutions of the total number of susceptible livestock, infected livestock and infected mosquitoes.

<p>(First Row) The theoretical prediction using the simplified force of infection. The values of the parameters used in years are as follows: <i>q</i>₁ = 0.05, <i>μ</i>₁ = (1/16) ∗ 360, <i>μ</i>₂ = 1/8, <i>β</i>₁₂ = 0.170, <i>β</i>₂₁ = 0.116, <i>ϵ</i>₂ = (1/4) ∗ 360, <i>α</i>′ = <i>α</i> = 256 and <i>m</i>₀ = 1.5. This gives <i>R</i>₀ = 1.0066. (Second Row) Comparison between theoretical predictions of PSD under the simplified and complex versions of the forces of infection. For the complex force of infection the new parameters are <i>α</i>₁ = 0.33, <i>α</i>₂ = 19, <i>m</i>₀ = 9.45 and , and <i>R</i>₀ = 1.0074. Note that description and sources of all model parameters are given in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005167#pntd.0005167.t001" target="_blank">Table 1</a>.</p

Power Spectra Density (PSD) for the variable <i>I</i>₂ (Eq (13)).

<p>a) Effects of vertical transmission efficiency on the PSD. Three-dimensional representation of the PSD when varying <i>R</i>₀ and the frequency for <i>q</i>₁ = 0.05 and <i>q</i>₅ = 0.5 in b) and c) respectively. Model parameter values used are as follows: <i>β</i>₁₂ = 0.170, <i>β</i>₂₁ = 0.116, <i>ϵ</i>₂ = (1/4) ∗ 360, <i>α</i>′ = <i>α</i> = 256, <i>μ</i>₂ = 1/8, <i>m</i>₀ = 1.5, <i>μ</i>₁ = (1/16) ∗ 360.</p

Temporal history of RVF outbreaks in some countries of Sub-Saharan Africa.

<p>In (a) and (b) the circles represent years of outbreaks occurrence in Kenya and South Africa [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005167#pntd.0005167.ref003" target="_blank">3</a>, <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005167#pntd.0005167.ref009" target="_blank">9</a>] and the prevalence indicated in the figure is not real, it is just for representation only since data on prevalence is not available. In (c) the circles represent the prevalence of disease outbreaks in Tanzania [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005167#pntd.0005167.ref007" target="_blank">7</a>].</p

Stochastic model for vector-host disease system.

<p>The parameter <i>m</i>₀ = <i>N</i>₁/<i>N</i>₂ is the ratio mosquitoes to hosts, and is for general forces of infections <i>λ</i>₂₁ and <i>λ</i>₁₂, and <i>α</i>′ = <i>α</i> is for standard forces of infections and .</p

Flow diagram of RVF model with both vertical and horizontal transmission.

<p>Susceptible livestock, <i>S</i>₂, acquire infection and move to compartment <i>I</i>₂ when they are bitten by an <i>Aedes</i> infectious mosquito <i>I</i>₁. They then recover with a constant per capita recovery rate to enter the recovered compartment, <i>R</i>₂, class. Susceptible mosquito vectors, <i>S</i>₁, become infected when they bite infectious livestock and progress to class <i>I</i>₁. The solid lines represent the transition between compartments and the dashed lines represent the transmission between different species.</p