RESUMO
BACKGROUND: The California Department of Public Health (CDPH) declared a pertussis epidemic on 23 June 2010. More cases were reported in 2010 (9146) than in any year since 1947. We describe the characteristics of pertussis epidemiology and disease from 986 reported cases in children in San Diego County (population 3.2 million). METHODS: Descriptive statistics were abstracted from CDPH pertussis case report forms that were completed by public health nurses investigating reports of positive laboratory results for pertussis and reports of illnesses compatible with pertussis. RESULTS: Of 1144 reported adult and pediatric cases, 753 (66%) were confirmed and 391 were probable/suspect. Children aged <19 years comprised 86% of all reported cases in San Diego County; of these, 22% were aged 11-18 years, 29% were aged 6-10 years, 27% were aged 1-5 years, and 22% were aged <1 year (with 70% aged <6 months). Case rates were highest in infants aged <6 months (651 per 100 000 population). Of those aged >1 year, the highest attack rates were in preschool children aged 1-5 years (114 per 100 000) and elementary school children aged 6-10 years (141 per 100 000). Of 51 children hospitalized, 82% were aged <6 months; 2 deaths occurred in these young infants. Paroxysmal cough was noted in over 70% of children in all age groups; post-tussive vomiting occurred in 36% (aged 11-18 years) to 57% (aged <6 months) of children. CONCLUSIONS: Pertussis vaccine efficacy may decrease more rapidly than previously believed, facilitating spread of pertussis in elementary school-aged children. The highest case rates and the only mortality occurred in infants aged <6 months.
RESUMO
We have carried out kinetics studies of spinach carbonic anhydrase (CA) using stopped-flow spectrophotometry at steady state and 13C-NMR exchange at chemical equilibrium. We found that the rate of CO2<-->HCO3- exchange catalyzed by spinach CA at pH 7.0 to be 3-5 times faster than the maximal kcat for either CO2 hydration or HCO3- dehydration at steady state, suggesting a rate-determining H+ transfer step in the catalytic mechanism. Correspondingly, we measured a pH-independent solvent deuterium isotope effect on kcat of approximately 2.0, and found that the rate of catalysis was significantly decreased at external buffer concentrations below 5 mM. Our results are consistent with a zinc-hydroxide mechanism of action with for spinach CA, similar to that of animal carbonic anhydrases. We have also collected X-ray absorption spectra of spinach CA. Analysis of the extended fine structure (EXAFS) suggests that the coordination sphere of Zn in spinach CA must have one or more sulfur ligands, in contrast to animal CAs which have only nitrogen and oxygen ligands. The models which best fit the data have average Zn-N(O) distances of 1.99-2.06 A, average Zn-S distances of 2.31--2.32 A, and a total coordination number of 4-6. We conclude that animal and spinach CAs are convergently evolved enzymes which are structurally quite different, but functionally equivalent.
