Trends in rural and urban deliveries and vaginal births: California 1998-2002.

CONTEXT: Pregnant women in rural areas may give birth in either rural or urban hospitals. Differences in outcomes between rural and urban hospitals may influence patient decision making. PURPOSE: Trends in rural and urban obstetric deliveries and neonatal and maternal mortality in California were compared to inform policy development and patient and provider decision making in rural health care settings. METHODS: Deliveries in California hospitals identified by the California Department of Health Services, Birth Statistical Master Files for years 1998 through 2002 were analyzed. Three groups of interest were created: rural hospital births to all mothers, urban hospital births to rural mothers, and urban hospital births to urban mothers. FINDINGS: Of 2,620,096 births analyzed, less than 4% were at rural hospitals. Neonatal death rates were significantly higher in babies born to rural mothers with no pregnancy complications who delivered a normal weight baby vaginally at an urban hospital compared to urban mothers delivering at an urban hospital (0.2 [CI 0.2-0.4] deaths per 1,000 births versus 0.1 [CI 0.1-0.1]). Logistic regression analysis showed that delivery in a rural hospital was a protective factor compared to urban mothers delivering in an urban hospital, with an odds ratio of 0.8 (CI 0.6-0.9). Maternal death rates were not different. CONCLUSIONS: Rural obstetric services in this period showed favorable neonatal and maternal safety profiles. This information should reassure patients considering a rural hospital delivery, and aid policy makers and health care providers striving to ensure access to obstetric services for rural populations.

Vaginal birth after cesarean in California: before and after a change in guidelines.

PURPOSE: In 1999 the American College of Obstetricians and Gynecologists (ACOG) adopted more-restrictive guidelines for vaginal birth after cesarean delivery (VBAC). This study assesses trends in VBAC in California and compares neonatal and maternal mortality rates among women attempting VBAC delivery or undergoing repeat cesarean delivery before and after this guideline revision. METHODS: The 1996 through 2002 California Birth Statistical Master Files were used to identify 386,232 California residents who previously gave birth by cesarean delivery and had a singleton birth planned in a California hospital. RESULTS: Attempted VBAC deliveries decreased significantly from 24% before to 13.5% after guideline revision (P <.001). Neonatal mortality rates per 1,000 live births for attempted VBAC deliveries were not different from repeat cesarean delivery rates among neonates weighing > or =1,500 g in either the study periods 1996 to 1999 or 2000 to 2002. Neonatal mortality rates for attempted VBAC deliveries were higher for repeat cesarean deliveries among neonates weighing <1,500 g in the same periods (attempted VBAC: 1996-1999, 253.2; 95% Poisson confidence interval [CI], 197.7-308.6; 2000-2002, 336.8; CI, 254.3-419.4; repeat cesarean delivery: 1996-1999, 59.1; CI, 48.3-69.9; 2000-2002, 60.5, CI, 48.4-72.5). Maternal death rates per 100,000 live births for attempted VBAC deliveries were similar for both periods (1996-1999, 2.0; CI, 0.1-11.0; 2000-2002, 8.5; CI, 1.0-30.6). CONCLUSIONS: Neonatal and maternal mortality rates did not improve despite increasing rates of repeat cesarean delivery during the years after the ACOG 1999 VBAC guideline revision. Women with infants weighing > or =1,500 g encountered similar neonatal and maternal mortality rates with VBAC or repeat cesarean delivery.

Influence of temperature and concentration of VectoBac on control of the salt-marsh mosquito, Ochlerotatus squamiger, in Monterey County, California.

Laboratory susceptibility bioassays were conducted to determine the efficacy of VectoBac TP (Bacillus thuringiensis var. israelensis [Bti]) at different concentrations and temperatures against the salt-marsh mosquito Ochlerotatus squamiger. Bioassays on late 3rd- and early 4th-stage larvae, read at 72 h and 14 degrees C produced an LD90 of 0.223 mg/liter, whereas more than double this dose was required to produce similar mortality at 6 degrees C. A field trial in the winter of 2001-02 of an aerially applied VectoBac TP formulation in Salinas, CA, corroborated laboratory bioassay observations by producing 97-100% control of Oc. squamiger at 72 h postapplication. Inconsistencies in mortality with field applications of VectoBac TP previously observed by North Salinas Valley Mosquito Abatement personnel were most likely caused by uneven application rates and varying temperatures and water volumes.

Pyrethroid tolerance in Culex pipiens pipiens var molestus from Marin County, California.

In May 2001 a sample of Culex pipiens pipiens variety molestus Forskål from Marin County, California, collected as larvae and reared to adults, was found to show reduced resmethrin and permethrin knock-down responses in bottle bioassays relative to a standard susceptible Cx. pipiens quinquefasciatus Say colony (CQ1). Larval susceptibility tests, using CQ1 as standard susceptible, indicated that the Marin mosquitoes had LC50 resistance ratios of 18.3 for permethrin, 12 for deltamethrin and 3.3 for pyrethrum. A colony of Marin was established and rapidly developed higher levels of resistance in a few generations after exposure to permethrin as larvae. These selected larvae were shown to cross-resist to lambda-cyhalothrin as well as to DDT. However, adult knock-down time in the presence of permethrin, resmethrin and pyrethrum was not increased after increase in tolerance to pyrethroids as larvae. Partial and almost complete reversion to susceptibility as larvae was achieved with S, S, S-tributylphosphorotrithioate and piperonyl butoxide (PBO), respectively, suggesting the presence of carboxylesterase and P450 monooxygenase mediated resistance. Insensitive target site resistance (kdr) was also detected in some Marin mosquitoes by use of an existing PCR-based diagnostic assay designed for Cx. p. pipiens L mosquitoes. Carboxylesterase mediated resistance was supported by use of newly synthesized novel pyrethroid-selective substrates in activity assays. Bottle bioassays gave underestimates of the levels of tolerance to pyrethroids of Marin mosquitoes when compared with mortality rates in field trials using registered pyrethroid adulticides with and without PBO. This study represents the first report of resistance to pyrethroids in a feral population of a mosquito species in the USA.

Differences in extent of genetic introgression between sympatric Culex pipiens and Culex quinquefasciatus (Diptera: Culicidae) in California and South Africa.

Comparisons of five morphological characters, 12 enzyme electrophoresis profiles, and Wolbachia pipientis infection rates were used to characterize populations of members of the Culex pipiens L. complex in California and South Africa. In South Africa, male phallosome DV/D ratio, male maxillary palp index, branching of siphonal seta 1a, the enzyme locus Mdhp-1, and W. pipientis infection rates proved highly diagnostic for separating Culex quinquefasciatus from Cx. pipiens phenotypes. In Johannesburg, where sympatric members of the Cx. pipiens complex were analyzed as one population, a significant Wahlund Effect was observed in the enzyme loci such as Ao, 6-Pgdh, Mdh-2, and Pgm. In California, all populations of the Cx. pipiens complex were in Hardy Weinberg equilibrium at all polymorphic enzyme loci examined. Additionally, in California, all populations had similar W. pipientis infection rates and appeared morphologically identical (except for DV/D ratio, in extreme north and south). These findings indicate that in South Africa, Cx. pipiens and Cx. quinquefasciatus remain as genetically distinct populations and behave as separate species. Conversely, in California, there is considerable genetic introgression between Cx. pipiens and Cx. quinquefasciatus, and they behave as a single species.

High level methoprene resistance in the mosquito Ochlerotatus nigromaculis (Ludlow) in central California.

In the summer of 1998, failures of methoprene field applications to control the mosquito Ochlerotatus nigromaculis (Ludlow) were noticed in several pastures in the outskirts of Fresno, California, USA. Effective control with methoprene had been achieved for over 20 years prior to this discovery. Susceptibility tests indicated that the Fresno Oc nigromaculis populations had developed several thousand-fold higher LC50 and LC90 tolerance levels to methoprene compared with methoprene-naïve populations. The synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate and 3-octylthio-1,1,1-trifluoro-2-propanone had little synergistic effect, suggesting that the mechanism of methoprene tolerance was not mediated by P450 monooxygenase or carboxylesterase enzyme degradation. As part of initiating a resistance management strategy, partial reversion back to methoprene susceptibility was achieved in a resistant population after six consecutive applications of Bacillus thuringiensis israelensis Goldberg & Marga coupled with two oil and two pyrethrum + PBO applications.