Severe <i>Citrus tristeza virus</i>Isolates from Eastern Mexico Are Related to the T36 Genotype Group

Citrus tristeza virus (CTV) outbreaks have been reported in the main citrus growing region of Mexico in the past four years. Recently, in eastern Mexico (the major citrus-growing region in the country), severe CTV isolates have been detected. However, the molecular identity of observed isolates remains unestablished. This research was undertaken to elucidate the molecular characterization of CTV populations spreading in this region and to compare it with phylogeny of existing isolates. Genotyping of 32 collected isolates was performed using reverse-transcription polymerase chain reaction (RT-PCR) with sequence analysis of the coat protein (CP) gene, putatively associated with pathogenicity. This protein is a 25 kDa major capsid protein, which forms a long virion body coating 95% of the particle length. A comparative sequence analysis was performed using CTV sequences from different geographical origins already published and deposited in the GenBank databases. Phylogenetic analysis showed that the degree of sequence divergence among isolates correlated with their pathogenicity. Based on the sequencing results, the collected isolates were categorizedn as mild or severe phylogenetic clusters, each being genetically distinct. The severe group was associated with either a-like or with a T36-like genotype. The latter group matched with the quick decline and stem pitting drastic symptoms observed in the field. This study identified the presence of severe CTV isolates related to the T36-like genotype and to the cause of quick decline and stem pitting in sweet orange propagated on sour orange rootstock. Knowledge derived from these analyses could serve to design management strategies for this disease and to understand the current epidemic outbreak in scenarios where the most efficient vector is present.

Ventilation of wards and nosocomial outbreak of severe acute respiratory syndrome among healthcare workers

Objective To identify valid measures for preventing outbreaks of severe acute respiratory syndrome (SARS) among protected healthcare workers in isolation units.Methods Architectural factors, admitted SARS cases and infection of healthcare workers in different isolation wards between January 30 and March 30, 2003 were analyzed.Results Four types of isolation wards were analyzed, including the ward where the thirty-first bed was located on the twelfth floor, the laminar flow ward in the Intensive Care Unit where the tenth bed was located on the fifteenth floor, the ward where the twenty-seventh bed was located on the thirteenth floor of the Lingnan Building, and thirty wards on the fourteenth to eighteenth floors of the Zhongshan Building. The ratios (m2/m3) of the area of the ventilation windows to the volume of the rooms were0, 0, 1:95 and 1:40, respectively. Numbers of SARS cases in the wards mentioned above were 1,1, 1 and 96, respectively. Total times of hospitalization were 43, 168, 110 and 1272 hours, respectively. The infection rates of the healthcare workers in the areas mentioned above were 73. 2% , 32.1%, 27.5% and 1.7%, respectively. The difference in the infection rates was of statistical significance.Conclusions Isolating SARS cases in wards with good ventilation could reduce the viral load of the ward and might be the key to preventing outbreaks of SARS among healthcare workers along with strict personal protection measures in isolation units.