A tuberculosis contact investigation involving a large number of contacts tested with interferon-gamma release assay at a nursing school: Kanagawa, Japan, 2012.

In May 2012, a teacher of a nursing school with about 300 staff members and students in Japan was diagnosed with sputum smear-positive pulmonary tuberculosis (TB), leading to an investigation involving nearly 300 contacts. We describe the contacts' closeness to the index TB patient and the likelihood of TB infection and disease. A case of TB was defined as an individual with positive bacteriological tests or by a physician diagnosis of TB. A latent TB infection (LTBI) case was defined as an individual who had a positive interferon-gamma release assay (IGRA). A total of 283 persons screened with IGRA were analysed. Eight persons (2.8%, 95% confidence interval [CI]: 1.2-5.4) tested positive by IGRA; one student who had intermediate (less than 10 hours) contact with the index patient was found to have pulmonary TB by chest X-ray. The positivity in IGRA among staff members with very close contact with the index patient (4 of 21, 19%, 95% CI: 5.4-42%) with a statistically significant relative risk of 17 (95% CI: 2.0-140) was high compared with that of the intermediate contacts (1 of 88, 1.1% [95% CI: 0.028-6.2]). There was a statistically significant trend in the risk of TB infection and closeness with the index patient among the staff members and students (P < 0.00022). In congregate settings such as schools, the scope of contact investigation may have to be expanded to detect a TB case among those who had brief contact with the index patient.

[A case of severe influenza (H1N1) 2009 virus pneumonia identified by virus culture instead of PCR].

A 70-year-old man was being treated for asthma and chronic obstructive pulmonary disease, which had been well controlled. He was seen at our emergency outpatient department on October 24, 2009, for respiratory distress and mild fever. Point-of-care testing for influenza, general bacteria, and acid-fast bacilli in the sputum, were negative. With antibiotics ineffective, his respiratory status worsened, requiring him to be intubated and ventilated mechanically. Steroid pulse therapy temporarily improved his condition, as confirmed by imaging studies, but he died on hospital day 38. Polymerase chain reaction (PCR) analysis of tracheal secretion and bronchial washings collected on hospital day 14 and 21 were negative for influenza (H1N1) 2009 virus, which was identified in a subsequent culture. Negative results for reverse transcriptase-PCR analysis leave (H1N1) 2009 virus unable to be diagnosed clinically. Culture tests and repeated PCR analysis have been done in cases of strongly suspected clinical infection to confirm results. Our case, in which the virus was identified by culture, suggests that the viral load may have been too low or the time of culture inappropriate.

Theoretical analysis for critical fluctuations of relaxation trajectory near a saddle-node bifurcation.

A Langevin equation whose deterministic part undergoes a saddle-node bifurcation is investigated theoretically. It is found that statistical properties of relaxation trajectories in this system exhibit divergent behaviors near a saddle-node bifurcation point in the weak-noise limit, while the final value of the deterministic solution changes discontinuously at the point. A systematic formulation for analyzing a path probability measure is constructed on the basis of a singular perturbation method. In this formulation, the critical nature turns out to originate from the neutrality of exiting time from a saddle point. The theoretical calculation explains results of numerical simulations.

Scale-free patterns at a saddle-node bifurcation in a stochastic system.

We demonstrate that scale-free patterns are observed in a spatially extended stochastic system whose deterministic part undergoes a saddle-node bifurcation. Remarkably, the scale-free patterns appear only at a particular time in relaxation processes from a spatially homogeneous initial condition. We characterize the scale-free nature in terms of the spatial configuration of the exiting time from a marginal saddle where the pair annihilation of a saddle and a node occurs at the bifurcation point. Critical exponents associated with the scale-free patterns are determined by numerical experiments.