Marginal structural model to evaluate the association between cumulative osteoporosis medication and infection using claims data

Due to the suboptimal persistence to osteoporosis (OP) treatment, factors triggering treatment discontinuation/switching may be causing time-varying confounding. BP treatment was associated with the risk of overall infection in opposite directions in the unweighted Cox model versus the weighted MSM. The discrepancy of effect estimates for overall infection in the MSM suggested there may be time-varying confounding.

INTRODUCTION

Due to the suboptimal persistence to osteoporosis (OP) treatment, factors triggering treatment discontinuation/switching may be affected by prior treatment and confound the subsequent treatment effect, causing time-varying confounding.

METHODS

In a US insurance database, the association between joint treatment of bisphosphonates (BP) and other OP medication and the incidence of infections among postmenopausal women was assessed using a marginal structural model (MSM). Stabilized weights were estimated by modeling treatment and censoring processes conditioning on past treatment, and baseline and time-varying covariates.

RESULTS

BP treatment was associated with the risk of overall infection in opposite directions in the unweighted Cox model {incidence rate ratio [IRR] [95% confidence interval (CI)] = 1.15 [1.14-1.17]} versus the weighted MSM [IRR (95% CI) = 0.79 (0.77-0.81)], but was consistently associated with a lower risk of serious infection in both the unweighted Cox model [IRR (95% CI] = 0.79 (0.78-0.81)) and the weighted MSM [IRR (95% CI) = 0.71 (0.68-0.75)]. Similar results were found when current and past treatments were simultaneously assessed.

CONCLUSIONS

The discrepancy of effect estimates for overall but not serious infection comparing unweighted models and MSM suggested analyses of composite outcomes with a wide range of disease severity may be more susceptible to time-varying confounding.

Determinants of anemia in postpartum HIV-negative women in Dar es Salaam, Tanzania

OBJECTIVE

The determinants of anemia during both pregnancy and postpartum recovery remain incompletely understood in sub-Saharan African women.

SUBJECTS/METHODS

In a prospective cohort study among pregnant women, we assessed dietary, biochemical, anthropometric, infectious and sociodemographic factors at baseline. In multivariate Cox proportional hazards models, we examined predictors of incident anemia (hemoglobin <11 g/dl) and iron deficiency anemia (anemia plus mean corpuscular volume <80fL), and recovery from anemia and iron deficiency anemia through 18 months postpartum at antenatal clinics in Dar es Salaam, Tanzania between 2001 and 2005. A total of 2364 non-anemic pregnant women and 4884 anemic women were enrolled between 12 and 27 weeks of gestation.

RESULTS

In total, 292 women developed anemia during the postpartum period and 165 developed iron deficiency anemia, whereas 2982 recovered from baseline anemia and 2044 from iron deficiency anemia. Risk factors for postpartum anemia were delivery complications (RR 1.6, 95% confidence interval (CI) 1.13, 2.22) and low postpartum CD4 cell count (RR 1.73, 95% CI 0.96, 3.17). Iron/folate supplementation during pregnancy had a protective relationship with the incidence of iron deficiency anemia. Absence of delivery complications, education status and iron/folate supplementation were positively associated with time to recovery from iron deficiency.

CONCLUSION

Maternal nutritional status during pregnancy, prenatal iron/folate supplementation, perinatal care, and prevention and management of infections, such as malaria, are modifiable risk factors for the occurrence of, and recovery from, anemia.