A controlled trial of sputum induction and routine collection methods for TB diagnosis in a South African community.

The diagnostic yield of pulmonary tuberculosis (TB) by sputum induction (SI) at the first point of contact with health services, conducted in all patients with suspected TB regardless of the ability to expectorate spontaneously, has not been evaluated. We compared the diagnostic yield of SI to routine sputum collection in a South African community setting. Ambulatory patients with suspected TB provided a 'spot' expectorated sputum sample, an SI sample by hypertonic (5 %) saline nebulization, and early morning expectorated sputum sample. The diagnostic yield of sputum smear microscopy and liquid culture (denominator all subjects with any positive Mycobacterium tuberculosis culture), and time-to-positivity of culture were compared between SI and expectorated samples. A total of 555 subjects completed the SI procedure, of whom 132 (24 %) were human immunodeficiency virus (HIV)-infected. One hundred and twenty-nine samples (129, 23 %) were M. tuberculosis culture-positive. The time-to-positivity of Mycobacteria Growth Indicator Tube (MGIT) culture was shorter for SI (median difference 2 days, p = 0.63) and for early morning expectorated sputum (median difference 2 days, p = 0.02) compared to spot expectorated sputum. However, there was no difference in the culture-positive diagnostic yield between SI and spot expectorated sputum [difference +0.7 %; confidence interval (CI) -7.0 to +8.5 %, p = 0.82] or SI and early morning expectorated sputum (difference +4.7 %; CI -3.2 to +12.5 %, p = 0.20) for all subjects or for HIV-infected subjects. SI reduces the time to positive M. tuberculosis culture, but does not increase the rate of positive culture compared to routine expectorated sputum collection. SI cannot be recommended as the routine collection method at first contact among ambulatory patients with suspected TB in high-burden communities.

Greenland Ice Sheet surface melt amplified by snowline migration and bare ice exposure.

Greenland Ice Sheet mass loss has recently increased because of enhanced surface melt and runoff. Since melt is critically modulated by surface albedo, understanding the processes and feedbacks that alter albedo is a prerequisite for accurately forecasting mass loss. Using satellite imagery, we demonstrate the importance of Greenland's seasonally fluctuating snowline, which reduces ice sheet albedo and enhances melt by exposing dark bare ice. From 2001 to 2017, this process drove 53% of net shortwave radiation variability in the ablation zone and amplified ice sheet melt five times more than hydrological and biological processes that darken bare ice itself. In a warmer climate, snowline fluctuations will exert an even greater control on melt due to flatter ice sheet topography at higher elevations. Current climate models, however, inaccurately predict snowline elevations during high melt years, portending an unforeseen uncertainty in forecasts of Greenland's runoff contribution to global sea level rise.

Modeling of subglacial hydrological development following rapid supraglacial lake drainage.

The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections. KEY POINTS: Model for subglacial hydrological analysis of rapid lake drainage eventsLimited subglacial channel growth during and following rapid lake drainagePersistence of distributed drainage in inland areas where channel growth is limited.