Epidemiology of airborne staphylococcal infection

Pathways to community transmission of COVID-19 due to rapid evaporation of respiratory virulets

HYPOTHESIS

The formation of virus-laden colloidal respiratory microdroplets - the sneeze or cough virulets and their evaporation driven miniaturization in the open air are found to have a significant impact on the community transmission of COVID-19 pandemic.

SIMULATION DETAILS

We simulate the motions and trajectories of virulets by employing laminar fluid flow coupled with droplet tracing physics. A force field analysis has been included considering the gravity, drag, and inertial forces to unleash some of the finer features of virulet trajectories leading to the droplet and airborne transmissions of the virus. Furthermore, an analytical model corroborates temperature (T) and relative humidity (RH) controlled droplet miniaturization.

RESULTS

The study elucidates that the tiny (1-50 µm) and intermediate (60-100 µm) size ranged virulets tend to form bioaerosol and facilitate an airborne transmission while the virulets of larger dimensions (300 to 500 µm) are more prone to gravity dominated droplet transmission. Subsequently, the mapping between the T and RH guided miniaturization of virulets with the COVID-19 cases for six different cities across the globe justifies the significant contribution of miniaturization-based bioaerosol formation for community transmission of the pandemic.

Exploring surface cleaning strategies in hospital to prevent contact transmission of methicillin-resistant Staphylococcus aureus

Background

Cleaning of environmental surfaces in hospitals is important for the control of methicillin-resistant Staphylococcus aureus (MRSA) and other hospital-acquired infections transmitted by the contact route. Guidance regarding the best approaches for cleaning, however, is limited.

Methods

In this study, a mathematical model based on ordinary differential equations was constructed to study MRSA concentration dynamics on high-touch and low-touch surfaces, and on the hands and noses of two patients (in two hospitals rooms) and a health care worker in a hypothetical hospital environment. Two cleaning interventions – whole room cleaning and wipe cleaning of touched surfaces – were considered. The performance of the cleaning interventions was indicated by a reduction in MRSA on the nose of a susceptible patient, relative to no intervention.

Results

Whole room cleaning just before first patient care activities of the day was more effective than whole room cleaning at other times, but even with 100% efficiency, whole room cleaning only reduced the number of MRSA transmitted to the susceptible patient by 54%. Frequent wipe cleaning of touched surfaces was shown to be more effective that whole room cleaning because surfaces are rapidly re-contaminated with MRSA after cleaning. Wipe cleaning high-touch surfaces was more effective than wipe cleaning low-touch surfaces for the same frequency of cleaning. For low wipe cleaning frequency (≤3 times per hour), high-touch surfaces should be targeted, but for high wipe cleaning frequency (>3 times per hour), cleaning should target high- and low-touch surfaces in proportion to the surface touch frequency. This study reproduces the observations from a field study of room cleaning, which provides support for the validity of our findings.

Conclusions

Daily whole room cleaning, even with 100% cleaning efficiency, provides limited reduction in the number of MRSA transmitted to susceptible patients via the contact route; and should be supplemented with frequent targeted cleaning of high-touch surfaces, such as by a wipe or cloth containing disinfectant.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-2120-z) contains supplementary material, which is available to authorized users.

Gloves, gowns and masks for reducing the transmission of meticillin-resistant Staphylococcus aureus (MRSA) in the hospital setting

BACKGROUND

Meticillin-resistant Staphylococcus aureus (MRSA; also known as methicillin-resistant S aureus) is a common hospital-acquired pathogen that increases morbidity, mortality, and healthcare costs. Its control continues to be an unresolved issue in many hospitals worldwide. The evidence base for the effects of the use of gloves, gowns or masks as control measures for MRSA is unclear.

OBJECTIVES

To assess the effectiveness of wearing gloves, a gown or a mask when contact is anticipated with a hospitalised patient colonised or infected with MRSA, or with the patient's immediate environment.

SEARCH METHODS

We searched the Specialised Registers of three Cochrane Groups (Wounds Group on 5 June 2015; Effective Practice and Organisation of Care (EPOC) Group on 9 July 2013; and Infectious Diseases Group on 5 January 2009); CENTRAL (The Cochrane Library 2015, Issue 6); DARE, HTA, NHS EED, and the Methodology Register (The Cochrane Library 2015, Issue 6); MEDLINE and MEDLINE In-Process & Other Non-Indexed Citations (1946 to June week 1 2015); EMBASE (1974 to 4 June 2015); Web of Science (WOS) Core Collection (from inception to 7 June 2015); CINAHL (1982 to 5 June 2015); British Nursing Index (1985 to 6 July 2010); and ProQuest Dissertations & Theses Database (1639 to 11 June 2015). We also searched three trials registers (on 6 June 2015), references list of articles, and conference proceedings. We finally contacted relevant individuals for additional studies.

SELECTION CRITERIA

Studies assessing the effects on MRSA transmission of the use of gloves, gowns or masks by any person in the hospital setting when contact is anticipated with a hospitalised patient colonised or infected with MRSA, or with the patient's immediate environment. We did not assess adverse effects or economic issues associated with these interventions.We considered any comparator to be eligible. With regard to study design, only randomised controlled trials (clustered or not) and the following non-randomised experimental studies were eligible: quasi-randomised controlled trials (clustered or not), non-randomised controlled trials (clustered or not), controlled before-and-after studies, controlled cohort before-after studies, interrupted time series studies (controlled or not), and repeated measures studies. We did not exclude any study on the basis of language or date of publication.

DATA COLLECTION AND ANALYSIS

Two review authors independently decided on eligibility of the studies. Had any study having been included, two review authors would have extracted data (at least for outcome data) and assessed the risk of bias independently. We would have followed the standard methodological procedures suggested by Cochrane and the Cochrane EPOC Group for assessing risk of bias and analysing the data.

MAIN RESULTS

We identified no eligible studies for this review, either completed or ongoing.

AUTHORS' CONCLUSIONS

We found no studies assessing the effects of wearing gloves, gowns or masks for contact with MRSA hospitalised patients, or with their immediate environment, on the transmission of MRSA to patients, hospital staff, patients' caregivers or visitors. This absence of evidence should not be interpreted as evidence of no effect for these interventions. The effects of gloves, gowns and masks in these circumstances have yet to be determined by rigorous experimental studies, such as cluster-randomised trials involving multiple wards or hospitals, or interrupted time series studies.

Roles of sunlight and natural ventilation for controlling infection: historical and current perspectives

BACKGROUND

Infections caught in buildings are a major global cause of sickness and mortality. Understanding how infections spread is pivotal to public health yet current knowledge of indoor transmission remains poor.

AIM

To review the roles of natural ventilation and sunlight for controlling infection within healthcare environments.

METHODS

Comprehensive literature search was performed, using electronic and library databases to retrieve English language papers combining infection; risk; pathogen; and mention of ventilation; fresh air; and sunlight. Foreign language articles with English translation were included, with no limit imposed on publication date.

FINDINGS

In the past, hospitals were designed with south-facing glazing, cross-ventilation and high ceilings because fresh air and sunlight were thought to reduce infection risk. Historical and recent studies suggest that natural ventilation offers protection from transmission of airborne pathogens. Particle size, dispersal characteristics and transmission risk require more work to justify infection control practices concerning airborne pathogens. Sunlight boosts resistance to infection, with older studies suggesting potential roles for surface decontamination.

CONCLUSIONS

Current knowledge of indoor transmission of pathogens is inadequate, partly due to lack of agreed definitions for particle types and mechanisms of spread. There is recent evidence to support historical data on the effects of natural ventilation but virtually none for sunlight. Modern practice of designing healthcare buildings for comfort favours pathogen persistence. As the number of effective antimicrobial agents declines, further work is required to clarify absolute risks from airborne pathogens along with any potential benefits from additional fresh air and sunlight.

CFD simulation of airborne pathogen transport due to human activities

Computational Fluid Dynamics (CFD) is an increasingly popular tool for studying the impact of design interventions on the transport of infectious microorganisms. While much of the focus is on respiratory infections, there is substantial evidence that certain pathogens, such as those which colonise the skin, can be released into, and transported through the air through routine activities. In these situations the bacteria is released over a volume of space, with different intensities and locations varying in time rather than being released at a single point. This paper considers the application of CFD modelling to the evaluation of risk from this type of bioaerosol generation. An experimental validation study provides a direct comparison between CFD simulations and bioaerosol distribution, showing that passive scalar and particle tracking approaches are both appropriate for small particle bioaerosols. The study introduces a zonal source, which aims to represent the time averaged release of bacteria from an activity within a zone around the entire location the release takes place. This approach is shown to perform well when validated numerically though comparison with the time averaged dispersion patterns from a transient source. However, the ability of a point source to represent such dispersion is dependent on airflow regime. The applicability of the model is demonstrated using a simulation of an isolation room representing the release of bacteria from bedmaking.

MRSA and the environment: implications for comprehensive control measures

Environmental contamination with methicillin-resistant Staphylococcus aureus (MRSA) is established soon after colonized or infected patients become resident. There are many studies that detail the mechanisms of spread and environmental survival of methicillin-susceptible Staphylococcus aureus (MSSA); this knowledge translates directly into the same findings for MRSA. The potential ubiquity of MRSA in a health-care setting poses challenges for decontamination. Whereas patients and medical staff are important sources for MRSA spread, the environmental burden may contribute significantly in various contexts. Effective control measures must therefore include consideration for MRSA in the environment.

Spread of methicillin-resistant Staphylococcus aureus in a neonatal intensive unit associated with understaffing, overcrowding and mixing of patients

Over the period May-June 1999, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) was registered in eight newborns in a neonatal intensive care unit (NICU) at the Department of Pediatrics, Ullevål University Hospital (UUH) in Oslo. Seven were infected or colonized with an indistinguishable strain, detected at the NICU, and one patient with a slightly different PFGE type (i.e. a subtype) was registered at the outpatient clinic. The MRSA strains resembled the sensitive, inbred 'Norwegian type' described four years earlier at UUH, showing a relatively low and heterogenic methicillin resistance (MIC 12-96 mg/L), and susceptibility to most other anti-staphylococcal agents. Before and during the outbreak, there was high activity, understaffing, overcrowding and a mix of patients; 42% of the staff were relatively untrained, and up to 62% (during weekends) were extra nursing staff, partly from other Scandinavian countries. All cases were isolated (air and contact isolation), and all other patients and personnel were treated as being exposed to MRSA (isolated from other departments) until the last patient had been identified, disinfection of all rooms was complete, and all screening samples from staff and other patients were negative. The NICU and the delivery suite were closed for one week for disinfection and screening. The outbreak ended after 34 days. Since then, two years later, no further cases have been detected in the NICU or the delivery suite.

Evaluation of bedmaking-related airborne and surface methicillin-resistant Staphylococcus aureus contamination

The number of airborne methicillin-resistant Staphylococcus aureus (MRSA) before, during and after bedmaking was investigated. Air was sampled with an Andersen air sampler in the rooms of 13 inpatients with MRSA infection or colonization. Sampling of surfaces, including floors and bedsheets, was performed by stamp methods. MRSA-containing particles were isolated on all the sampler stages-stage 1 (>7 microm diameter) to stage 6 (0.65-1.1 microm). The MRSA-containing particles were mostly 2-3 microm diameter before bedmaking and >5 microm during bedmaking. The number was significantly higher 15 min after bedmaking than during the resting period, but the differences in counts after 30 and 60 min were not significant. MRSA was detected on many surfaces. The results suggest that MRSA was recirculated in the air, especially after movement. To prevent airborne transmission, healthcare staff should exercise great care to disinfect inanimate environments. Further studies will be needed to confirm the level of MRSA contamination of air during bedmaking and establish measures for prevention of airborne transmission.

Is infection control an academic study?

This editorial aims to answer the question of whether infection control is an academic specialty. By considering the consequences of a lack of infection control in terms of patient morbidity and mortality and hence cost, it is easy to establish the importance of the area. Infection control embraces not only developing policies for preventing the physical spread of a micro-organism but also prophylactic therapy such as vaccination and therapeutic measures such as antibiotics. Infection control not only applies to localized infection in hospital due to antibiotic resistant microbes but also to the community. Bacteria such as Helicobacter pylori and Chlamydia pneumoniae and the viruses hepatitis B, hepatitis C, human lymphotropic virus type 1, Epstein-Barr viruses and human papilloma virus have been implicated in diseases not previously thought to have an infectious origin. Coping with these problems is clearly an academic area.

The effect of increased bed numbers on MRSA transmission in acute medical wards

An 18-month prospective survey was performed to examine the effect of adding a fifth bed to four-bedded bays in three acute medical wards on colonization by methicillin-resistant Staphylococcus aureus (MRSA). Screening procedures were in accordance with the UK national guidelines. All patients newly colonized with MRSA were visited, and their bed location determined. Data from the five-bedded bays were compared with those from four-bedded bays in similar wards. Potential routes of transmission were investigated by observational surveys. The relative risk of colonization in five-bedded medium dependency bays was 3.15 compared with that of similar four-bedded bays (P < 0.005), and in five-bedded low dependency bays was 3.16 (P < 0.005). Increasing the number of beds in a fixed area heightens the risk of cross-infection with MRSA.

Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

A six month prospective study was carried out in a surgical intensive care unit (SICU) of a university hospital to assess the incidence and routes of exogenous colonization by Staphylococcus aureus. A total of 157 patients were included in the study. One thousand one hundred and eleven specimens (nasal, surgical wound swabs, tracheal secretions obtained on admission and once a week thereafter, and all clinical specimens) were collected over a four month period from patients without nasal decontamination (A). They were compared with 729 specimens collected over a two month period from patients treated with nasal mupirocin ointment (B). All S. aureus strains were typed by restriction fragment length polymorphism (RFLP) pulsed-field gel electrophoresis after SmaI macrorestriction. The nasal colonization rates on admission were 25.5 and 32.7% in groups A and B, respectively. Thirty-one untreated patients (31.3%) and three patients (5.1%) treated with nasal ointment, acquired the nasal S. aureus in the SICU (P = 0.00027). Nasal carriers were more frequently colonized in the bronchopulmonary tract (Bp) and surgical wound (Sw) (62%) than patients who were not nasal carriers (14%) (P < 0.00001). The patterns were identical for nasal, Bp and Sw strains from the same patient. RFLP analysis characterized seven epidemic strains of methicillin-resistant S. aureus (MRSA) which colonized 60% of group A and 9% of group B patients (P < 0.00001). The bronchopulmonary tract infection rate was reduced in group B (P = 0.032). In conclusion, in an SICU, nasal carriage of S. aureus appeared to be the source of endogenous and cross-colonization. The use of nasal mupirocin ointment reduced the incidence of Bp and Sw colonization, as well as the MRSA infection rate.

Airborne bacteria and surgical infection

From the inception of modern surgery, the significance of airborne microbes to surgical infection has been controversial. The success of aseptic methods led the majority of surgeons early in this century to discount the airborne route. Despite aseptic disciplines, a significant level of infection continued and from 1930 onwards renewed attention was directed towards the air. Many studies over the following 25 years produced anecdotal and suggestive evidence that this was relevant and that a reduction in surgical sepsis followed a reduction in the numbers of airborne bacteria in the operating room. To this day, however, there has been no wholly satisfactory demonstration of this. Such a demonstration requires comparison of the outcome of a considerable number of surgical operations performed during the same period by the same surgeons under conditions which differ only in the levels of air contamination. Recent developments in orthopedics have resulted in large numbers of essentially similar operations on a site susceptible to infection but free from sources of bacteria within itself. Under these conditions, there is evidence that the numbers of bacteria contaminating the would at the end of the procedure are substantially fewer when the levels of airborne bacteria are reduced.

Staphylococcus aureus in rural drinking water

Coagulase-positive Staphylococcus aureus was isolated from over 6% of 320 rural drinking water specimens. Well water was the most common source examined. The presence of S. aureus was not found to correlate with the presence of coliform bacteria. Strains of Staphylococcus that produced enterotoxin A were found in 40% of the samples containing S. aureus. Additional studies showed that faucet aerator screens were common sources of high cell densities of S. aureus.

Dispersal and transfer of Staphylococcus aureus in an isolation ward for burned patients

The dispersal of Staphylococcus aureus from burned patients, the relation between nasal carriage by the staff and exposure to airborne Staph. aureus, and the transfer of Staph. aureus-carrying particles within the ward have been studied. The dispersal of Staph. aureus from burned patients was correlated to the size of the burn wound. The median values varied from 21 c.f.u./m.(2)/hr. for patients with small burns to 453 c.f.u./m.(2)/hr. for extensively burned patients. The size of the dispersed particles appeared to be smaller than that usually found in hospital wards. Carriage of nasal strains by the staff was correlated to the air counts; the number of patient sources did not seem to be of great importance. The transfer of Staph. aureus within the ward was at least 6 to 20 times that which would have been expected if transfer was due to air movement only.

Isolation for the control of infection in skin wards

An isolation policy in a hospital for skin diseases is reported. Patients carrying penicillin- and tetracycline-resistant organisms were to be isolated in single rooms, though barrier nursing was not practised. The policy failed because the single beds rapidly became blocked with long-stay patients and because even in a single-bed unit patients acquired staphylococci within 3-7 days of admission. Patients with skin diseases often do not feel ;ill' and resent isolation.

Airborne staphylococci in the surgical ward

The air of a subdivided surgical ward was sampled by the exposure of culture plates for 12 hr. periods 5 days a week.

A number of ‘broadcasts’ of airborneStaphylococcus aureuswere observed; many of these were of very short duration. A single person could be recognized as responsible for 22 of the 33 broadcasts; in all cases dispersal seemed to be from carrier sites rather than from infected lesions.

There was little spread of the staphylococci between the 4 rooms of the ward. The frequency of nasal carriage of tetracycline-resistantS. aureusincreased from 6·2% in patients examined during their 1st week to 13·2% in those examined in their 4th week in the ward; the rate for allS. aureusdeclined from 31·3 to 26·4%.

It is suggested that the long-period exposure of culture plates for the collection of airborne staphylococci may be useful in monitoring some aspects of hospital hygiene.