Grading of a positive sputum smear and the risk of Mycobacterium tuberculosis transmission.

SETTING: After the diagnosis of a case of tuberculosis (TB), contact tracing is directed by the risk of transmission, for which sputum acid-fast bacilli (AFB) staining results are highly relevant. Limited data are available on the effect of the degree of acid-fast positivity, of a polymerase chain reaction (PCR) result or of bronchoalveolar lavage (BAL) fluid results on the risk of transmission. OBJECTIVES: To investigate factors associated with TB transmission, focusing on quantitative sputum smear results. DESIGN: Retrospective study of contact investigations performed over a period of 5 years in a Dutch Municipal Health Service among all index patients with TB, and the tuberculin skin test and chest radiography results in contacts. Three definitions of transmission were used: ≥ 1 or ≥ 5 contacts with positive TST or active TB in contacts. RESULTS: The highest (+4/+5) sputum AFB grades were associated with the highest relative risk (≥ 8) of extensive transmission or active TB among contacts. Novel risk factors observed were employment or school attendance, positive PCR of sputum and positive AFB staining of BAL fluid. Pulmonary symptoms, infiltrate or cavity and positive AFB sputum stain were also associated with transmission, confirming previous studies. CONCLUSION: The risk factors observed in this study may aid in the extension of contact investigations.

Quantitative assessment of ammonia-oxidizing bacterial communities in the epiphyton of submerged macrophytes in shallow lakes.

In addition to the benthic and pelagic habitats, the epiphytic compartment of submerged macrophytes in shallow freshwater lakes offers a niche to bacterial ammonia-oxidizing communities. However, the diversity, numbers, and activity of epiphytic ammonia-oxidizing bacteria have long been overlooked. In the present study, we analyzed quantitatively the epiphytic communities of three shallow lakes by a potential nitrification assay and by quantitative PCR of 16S rRNA genes. On the basis of the m(2) of the lake surface, the gene copy numbers of epiphytic ammonia oxidizers were not significantly different from those in the benthic and pelagic compartments. The potential ammonia-oxidizing activities measured in the epiphytic compartment were also not significantly different from the activities determined in the benthic compartment. No potential ammonia-oxidizing activities were observed in the pelagic compartment. No activity was detected in the epiphyton of Chara aspera, the dominant submerged macrophyte in Lake Nuldernauw in The Netherlands. The presence of ammonia-oxidizing bacterial cells in the epiphyton of Potamogeton pectinatus was also demonstrated by fluorescent in situ hybridization microscopy images. By comparing the community composition as assessed by the 16S rRNA gene PCR-denaturing gradient gel electrophoresis approach, it was concluded that the epiphytic ammonia-oxidizing communities consisted of cells that were also present in the benthic and pelagic compartments. Of the environmental parameters examined, only the water retention time, the Kjeldahl nitrogen content, and the total phosphorus content correlated with potential ammonia-oxidizing activities. None of these parameters correlated with the numbers of gene copies related to ammonia-oxidizing betaproteobacteria.