Can you really say air is a limited vector with so few samples and so little air volume?
A more accurate statement would be to calculate which bacterial concentration or greater, at which specific prevalence or greater, is unlikely given the set of negative passive and active air samples for a given level of confidence. We are in the process of making such calculations.
Do you feel birds or insects landed on the passive air collectors which may have increased their positives?
We cannot rule out that contact by birds, insects, or other environmental factors may have contributed to some positive detections on the passive air collectors. However, these interactions were not directly measured in this study, so their impact is unknown.
Did you use any to enhance adhesion to gauze for air sampling?
No. The gauze was deployed without any adhesion enhancers and was suspended between two wooden stakes for approximately 24 hours during sampling.
Do you think the passive air method improves chances because of capturing the daily cycle of air changing direction?
The passive air method used in this study (sheet of gauze) would presumably perform better during conditions of non-zero mph wind velocity in order to impinge the airborne bacteria onto the material. Merely changing wind direction would unlikely increase bacterial deposition, all things equal, for this study region, but sampling for 24 hours compared to 1 hour is likely a big factor in detection success.
For active air sampling was the basis for detection only PCR or sequence Target based or dependent on cultural viable recovery?
Detection in active air samples was based on culture-dependent methods, requiring viable recovery of the organism.
I’m wondering about the temporal scale of the air sampling. With collections limited to about 24 hours, how do you account for the much longer crop exposure period of 20–70 days when interpreting the data?
The 24-hour air sampling period represents a short-term snapshot of airborne contamination under prevailing field conditions and cannot directly integrate exposure over the full 20–70 day crop growth period. Extending deployment was not feasible due to loss of bacterial viability on the sampling material. To partially address temporal variability, air sampling was repeated across multiple time points and environmental conditions throughout the growing season. Across these sampling events, STEC detection in air samples was consistently low, suggesting that airborne transmission is not a major contributor over the production period. A more direct assessment would involve concurrent air and crop sampling; however, crop sampling was not permitted on produce farms under our agreements. As an alternative, we sampled grape leaves in vineyards and observed a low STEC prevalence (2.4%; 2/85), consistent with the low recovery from passive air samples.
Since air monitoring results did not reveal positives with any significance, does that mean the deposition distance beliefs affecting buffer zones should be reevaluated? Buffers reduced?
The CALS study was not designed to establish or recommend specific buffer distances between animal operations and produce fields. Existing guidance and policies are intentionally flexible to account for site-specific conditions, and buffer decisions are best informed by a combination of risk assessment, environmental factors, and current best practices.
So air samples were pulled into the active air samplers for 1hr and then attempted culture recovery? Not too stressful or lethal from dedication?
We wet the agar prior to use in the active sampler to help minimize desiccation during the hour of sampling.
What are average wind speeds in the sample areas?
The average wind speed in the air sampling areas was 2.55 m/s (5.7 mph), based on 24-hour measurements. Wind speeds ranged from 0 to 6.6 m/s (0 to 14.8 mph).
Were the air samples taken near features of interest? Passive air samples at 1.4% could be low or high, but it seems like that could be highly influenced by where the air samples were taken.
Air samples were collected near features of interest and under conditions likely to promote airborne transport. Sampling locations included areas with high dust and wind, sites adjacent to compost operations or rangeland with cattle, and areas where higher numbers of STEC-positive samples had previously been identified. Samples were collected across multiple site types, including public lands, produce farms, vineyards, and compost facilities.
What do you make of the fact that this study showed air to be a minimal vector, but the Yuma study showed air (actually dust) to be a very significant vector?
CALS detected very few pathogens in air samples collected in the California Central Coast region, suggesting that airborne movement may not have been a major pathway for pathogen dissemination under the conditions evaluated in this study area and timeframe. Longitudinal studies reflect regional and local environmental conditions, agricultural practices, weather patterns, and other site-specific factors. Therefore, caution should be exercised when comparing findings across different regions or extrapolating results beyond the specific study area.
Why such a short time to collect air samples (both active and passive)? Do you think the air sampling methodology could have been a factor for the active air? Given the historically low prevalence this doesn’t seem likely to find something. Like longer exposure times would have had different results?
Air sampling duration can influence the likelihood of pathogen detection, particularly when environmental prevalence is low. The passive air sampling timeframe used in CALS was generally consistent with approaches used in previous environmental microbiology studies. Based on results from a previous study, the volume of air sampled with the active air sampler in CALS was low for STEC detection when the prevalence in air is low. The active air sample results were useful for determining aerobic plate counts in the air throughout the study region. The extent to which air sampling methodology affects STEC detection in agricultural environments remains an important area for future research.
Without air, how does one explain distance?
Presumably STEC can be transported long distances by, for example, infected free-ranging wildlife (avian, terrestrial), transporting infected livestock, moving surface water like tailwater in ditches and rivers, contaminated equipment and other fomites that are moved between locations, contaminated manure products being transported between locations, and infected humans traveling throughout the Salinas region.