Review and comparison between the Wells-Riley and dose-response approaches to risk assessment of infectious respiratory diseases

Infection risk assessment is very useful in understanding the transmission dynamics of infectious diseases and in predicting the risk of these diseases to the public. Quantitative infection risk assessment can provide quantitative analysis of disease transmission and the effectiveness of infection control measures. The Wells-Riley model has been extensively used for quantitative infection risk assessment of respiratory infectious diseases in indoor premises. Some newer studies have also proposed the use of dose-response models for such purpose. This study reviews and compares these two approaches to infection risk assessment of respiratory infectious diseases. The Wells-Riley model allows quick assessment and does not require interspecies extrapolation of infectivity. Dose-response models can consider other disease transmission routes in addition to airborne route and can calculate the infectious source strength of an outbreak in terms of the quantity of the pathogen rather than a hypothetical unit. Spatial distribution of airborne pathogens is one of the most important factors in infection risk assessment of respiratory disease. Respiratory deposition of aerosol induces heterogeneous infectivity of intake pathogens and randomness on the intake dose, which are not being well accounted for in current risk models. Some suggestions for further development of the risk assessment models are proposed.

PRACTICAL IMPLICATIONS

This review article summarizes the strengths and limitations of the Wells-Riley and the dose-response models for risk assessment of respiratory diseases. Even with many efforts by various investigators to develop and modify the risk assessment models, some limitations still persist. This review serves as a reference for further development of infection risk assessment models of respiratory diseases. The Wells-Riley model and dose-response model offer specific advantages. Risk assessors can select the approach that is suitable to their particular conditions to perform risk assessment.

Physical interventions to interrupt or reduce the spread of respiratory viruses

BACKGROUND

Viral epidemics or pandemics of acute respiratory infections like influenza or severe acute respiratory syndrome pose a world-wide threat. Antiviral drugs and vaccinations may be insufficient to prevent catastrophe.

OBJECTIVES

To systematically review the effectiveness of physical interventions to interrupt or reduce the spread of respiratory viruses.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, issue 2); MEDLINE (1966 to May 2009); OLDMEDLINE (1950 to 1965); EMBASE (1990 to May 2009); and CINAHL (1982 to May 2009).

SELECTION CRITERIA

We scanned 2958 titles, excluded 2790 and retrieved the full papers of 168 trials, to include 59 papers of 60 studies. We included any physical interventions (isolation, quarantine, social distancing, barriers, personal protection and hygiene) to prevent transmission of respiratory viruses. We included the following study designs: randomised controlled trials (RCTs), cohorts, case controls, cross-over, before-after, and time series studies.

DATA COLLECTION AND ANALYSIS

We used a standardised form to assess trial eligibility. RCTs were assessed by: randomisation method; allocation generation; concealment; blinding; and follow up. Non-RCTs were assessed for the presence of potential confounders, and classified into low, medium, and high risks of bias.

MAIN RESULTS

The risk of bias for the four RCTs, and most cluster RCTs, was high. The observational studies were of mixed quality. Only case-control data were sufficiently homogeneous to allow meta-analysis.The highest quality cluster RCTs suggest respiratory virus spread can be prevented by hygienic measures, such as handwashing, especially around younger children. Additional benefit from reduced transmission from children to other household members is broadly supported in results of other study designs, where the potential for confounding is greater. Six case-control studies suggested that implementing barriers to transmission, isolation, and hygienic measures are effective at containing respiratory virus epidemics. We found limited evidence that N95 respirators were superior to simple surgical masks, but were more expensive, uncomfortable, and caused skin irritation. The incremental effect of adding virucidals or antiseptics to normal handwashing to decrease respiratory disease remains uncertain. Global measures, such as screening at entry ports, were not properly evaluated. There was limited evidence that social distancing was effective especially if related to the risk of exposure.

AUTHORS' CONCLUSIONS

Many simple and probably low-cost interventions would be useful for reducing the transmission of epidemic respiratory viruses. Routine long-term implementation of some of the measures assessed might be difficult without the threat of a looming epidemic.

[Papillomavirus infection of the upper respiratory tract and anogenital region in children. Transmission routes and possibilities for prevention]

This review of present-day knowledge of etiology of laryngeal papillomatosis is focused on transition routes of papillomavirus infection in children and possibilities for its prevention.

Preventing the spread of acute respiratory viral infections

Acute respiratory tract infections (ARIs) caused by viruses are not easily treated, so public health measures to prevent transmission are important. Most ARIs cause only mild, self-limiting illnesses. Nevertheless, they account for considerable loss of time from school and work, disrupting education and affecting the economy. The role of hygiene, especially handwashing in reducing the risk of infection, was established in research studies in the 1970s, but few members of the public or health professionals appear to recognise the importance of hand hygiene. The emergence of new, more serious ARIs may renew interest in hygiene, particularly hand hygiene, as an important preventive measure.

Infectious disease and boxing

There are no unique boxing diseases but certain factors contributing to the spread of illnesses apply strongly to the boxer, coach, and the training facility. This article examines the nature of the sport of boxing and its surrounding environment, and the likelihood of spread of infection through airborne, contact, or blood-borne routes of transmission. Evidence from other sports such as running, wrestling, and martial arts is included to help elucidate the pathophysiologic elements that could be identified in boxers.

Association of Stenotrophomonas maltophilia infection with lower airway disease in the horse: a retrospective case series

Stenotrophomonas maltophilia is being reported with increasing frequency as a human nosocomial pathogen, especially among immuno-compromised patients. To the authors' knowledge, this pathogen has not previously been associated with lower airway disease in the horse. In this paper the clinical findings, laboratory diagnosis and response to treatment of seven cases of respiratory infection with S. maltophilia in horses, presented at three equine referral hospitals in Denmark in 2007, are described. In all cases there was a clinical history of chronic coughing and abundant mucopurulent exudate was observed in the lower trachea on endoscopy. On culture of tracheal aspirate, grey, slow-growing colonies, identified as S. maltophilia by both API 20NE identification and 16s ribosomal DNA sequencing, were identified. All isolates had a similar antibiotic susceptibility pattern characterised by resistance to all penicillins and cephalosporins, and to imipenem, gentamicin, amikacin and rifampicin. Ribotyping and pulsed-field gel electrophoresis of the S. maltophilia isolates from different patients indicated that they were either indistinguishable or closely related. This study indicates that S. maltophilia can be associated with chronic lower airway disease in the horse and provides useful initial insights into the diagnosis, therapy and epidemiology of this novel condition.

Molecular epidemiological study of Moraxella catarrhalis isolated from nosocomial respiratory infection patients in a community hospital in Japan

BACKGROUND

Moraxella catarrhalis, occasionally, plays the essential role in nosocomial respiratory infection (NRI). Few studies have reported the route by which this organism spreads in a nosocomial infection outbreak. We identified characteristics of the strains isolated from NRI and attempted to reveal the potential nosocomial transmission routes.

METHODS

A follow-up study has been performed in a Japanese community hospital between July 2002 and January 2003. M. catarrhalis clinical isolates were identified and beta-lactamase production test as well as the minimal inhibitory concentrations (MICs) have been examined. Pulsed-field gel electrophoresis (PFGE) and the multi locus sequence typing method (MLST) have been introduced as the effective "fingerprinting" methods.

RESULTS

A total of 29 strains were isolated from 17 participants; 7 independent DNA fragment patterns were detected by PFGE. Pattern B (defined in this study) was dominant, and was detected both in strains from a health care worker (HCW) and inpatients. In the 9 selected strains analyzed by MLST, 7 unique MLST types were identified, which showed the congruence with the results of PFGE results.

CONCLUSION

Epidemiological analysis proved the transmission route from patient to patient, and suggested that more studies should be focused on identifying the possible transmission route between HCWs and inpatients.

Identification and characterization of a new orthoreovirus from patients with acute respiratory infections

First discovered in the early 1950s, reoviruses (respiratory enteric orphan viruses) were not associated with any known disease, and hence named orphan viruses. Recently, our group reported the isolation of the Melaka virus from a patient with acute respiratory disease and provided data suggesting that this new orthoreovirus is capable of human-to-human transmission and is probably of bat origin. Here we report yet another Melaka-like reovirus (named Kampar virus) isolated from the throat swab of a 54 year old male patient in Kampar, Perak, Malaysia who was suffering from high fever, acute respiratory disease and vomiting at the time of virus isolation. Serological studies indicated that Kampar virus was transmitted from the index case to at least one other individual and caused respiratory disease in the contact case. Sequence analysis of the four small class genome segments indicated that Kampar and Melaka viruses are closely related. This was confirmed by virus neutralization assay, showing an effective two-way cross neutralization, i.e., the serum against one virus was able to neutralize the other. Although the exact origin of Kampar virus is unknown, epidemiological tracing revealed that the house of the index case is surrounded by fruit trees frequently visited by fruit bats. There is a high probability that Kampar virus originated from bats and was transmitted to humans via bat droppings or contaminated fruits. The discovery of Kampar virus highlights the increasing trend of emergence of bat zoonotic viruses and the need to expand our understanding of bats as a source of many unknown viruses.

Emerging Chlamydial Infections

Chlamydiae are important intracellular bacterial pathogens of vertebrates. In the last years, novel members of this group have been discovered: Parachlamydia acanthamoebae and Simkania negevensis seems to be emerging respiratory human pathogens, while Waddlia chondrophila might be a new agent of bovine abortion. Various species have been showed to infect also the herpetofauna and fishes, and some novel chlamydiae are endosymbionts of arthropods. In addition, molecular studies evidenced a huge diversity of chlamydiae from both environmental and clinical samples, most of such a diversity could be formed by novel lineages of chlamydiae. Experimental studies showed that free-living amoebae may support multiplication of various chlamydiae, then could play an important role as reservoir/vector of chlamydial infections. Here we reviewed literature data concerning chlamydial infections, with a particular emphasis on the novely described chlamydial organisms.

Oral supplementation with L-lysine did not prevent upper respiratory infection in a shelter population of cats

Cats in animal shelters are highly susceptible to infection by feline herpesvirus (FHV) by virtue of their stress and close proximity to other cats. Animal shelters take several different approaches to prevent FHV-related upper respiratory infections (URIs), including empirically treating all cats with L-lysine, a supplement believed to prevent the replication of FHV and, therefore, manifestations of herpesvirus infections. In this study we tested oral supplementation of L-lysine as a means to prevent URIs. One hundred and forty-four cats were treated with L-lysine in a small amount of canned food once daily. A 'no treatment' group of 147 cats received no lysine during the course of the study. The development of conjunctivitis or URI was tracked between the two groups. In all measures, there was no effect between the two groups, suggesting that lysine was not able to prevent URI or conjunctivitis in our shelter situation. Cats entering shelters encounter stressors that may make them more susceptible to FHV reactivation or infection. Infection control and control of fomite transmission are also key to keeping cats healthy in a group housing situation. The finding that lysine did not prevent URI in this animal shelter suggests that shelters may better use their resources by finding ways to decrease stress among their feline population, focusing on proper infection control measures, and limiting fomite transmission of disease.

A study quantifying the hand-to-face contact rate and its potential application to predicting respiratory tract infection

A substantial portion of human respiratory tract infection is thought to be transmitted via contaminated hand contact with the mouth, eyes, and/or nostrils. Thus, a key risk factor for infection transmission should be the rate of hand contact with these areas termed target facial membranes. A study was conducted in which 10 subjects were each videotaped for 3 hr while performing office-type work in isolation from other persons. The number of contacts to the eyes, nostrils, and lips was scored during subsequent viewing of the tapes. The total contacts per subject had sample mean x = 47 and sample standard deviation s = 34. The average total contact rate per hour was 15.7. The authors developed a relatively simple algebraic model for estimating the dose of pathogens transferred to target facial membranes during a defined exposure period. The model considers the rate of pathogen transfer to the hands via contact with contaminated environmental surfaces, and the rate of pathogen loss from the hands due to pathogen die-off and transfer from the hands to environmental surfaces and to target facial membranes during touching. The estimation of infection risk due to this dose also is discussed. A hypothetical but plausible example involving influenza A virus transmission is presented to illustrate the model.

Risk management of febrile respiratory illness in emergency departments

Febrile Respiratory Illness (FRI) is defined as a new or worsening episode of either cough or shortness of breath, presenting with fever (temperature 38 degrees C or higher) or chills in the previous 24 hours. Some FRI could cause large outbreaks of potentially life-threatening diseases (multi- or extensively drug resistant MTB, SARS, pandemic influenza) if not adequately controlled. Emergency Departments (EDs) are preferential sites of disease transmission because of the presence of both infectious and susceptible patients in the same space, the lack of rapid isolation of infectious patients, and the frequent and close contacts among patients and HCWs often not protected by PPE. The management of risk of FRI transmission is thus extremely important in EDs, where all procedures of infection control should be in place and continually monitored and assessed. In this article the main procedures for the management of risk of FRI transmission in EDs are described and discussed.

Social contacts and mixing patterns relevant to the spread of infectious diseases

BACKGROUND

Mathematical modelling of infectious diseases transmitted by the respiratory or close-contact route (e.g., pandemic influenza) is increasingly being used to determine the impact of possible interventions. Although mixing patterns are known to be crucial determinants for model outcome, researchers often rely on a priori contact assumptions with little or no empirical basis. We conducted a population-based prospective survey of mixing patterns in eight European countries using a common paper-diary methodology.

METHODS AND FINDINGS

7,290 participants recorded characteristics of 97,904 contacts with different individuals during one day, including age, sex, location, duration, frequency, and occurrence of physical contact. We found that mixing patterns and contact characteristics were remarkably similar across different European countries. Contact patterns were highly assortative with age: schoolchildren and young adults in particular tended to mix with people of the same age. Contacts lasting at least one hour or occurring on a daily basis mostly involved physical contact, while short duration and infrequent contacts tended to be nonphysical. Contacts at home, school, or leisure were more likely to be physical than contacts at the workplace or while travelling. Preliminary modelling indicates that 5- to 19-year-olds are expected to suffer the highest incidence during the initial epidemic phase of an emerging infection transmitted through social contacts measured here when the population is completely susceptible.

CONCLUSIONS

To our knowledge, our study provides the first large-scale quantitative approach to contact patterns relevant for infections transmitted by the respiratory or close-contact route, and the results should lead to improved parameterisation of mathematical models used to design control strategies.

Patterns of influenza infections among different risk groups in Brazil

Influenza virus infections are associated with high morbidity and mortality. Influenza activity varies worldwide, and regional detection is influenced by geographic conditions, demographic and patient-risk factors. We assessed influenza activity and patterns of seasonality during three consecutive years (2001-2003) in three risk groups in São Paulo city. Four-hundred-twelve outpatients with acute respiratory infection were subjected to epidemiological, clinical and laboratory investigations; these included community population (N=140), health-care workers (N=203), and renal-transplanted patients (N=69). Nasal wash samples were tested by direct fluorescent assay for influenza, parainfluenza, adenovirus, and respiratory syncytial virus. Overall Influenza positivity was 21%, and a progressive decline was observed in all groups over time. Influenza A and B co-circulated at the same time in 2001 and 2002, but not in 2003. Low influenza-vaccination rates (19%) were reported by health-care workers. Unexpected low levels of etiological agents were detected in renal-transplanted patients, and infected cases were less symptomatic than immunocompetent patients. Based on this study, we conclude that health-care worker-immunization programs should be implemented and the clinical patterns of infected influenza patients should be used as a guide for better case-definition criteria for adequate influenza surveillance, particularly for renal-transplant patients.

Filters reduce the risk of bacterial transmission from contaminated heated humidifiers used with CPAP for obstructive sleep apnea

RATIONALE

The treatment of choice for obstructive sleep apnea (OSA) is nasal continuous positive airway pressure (nCPAP) during sleep, but dryness of the upper airway compromises compliance. Heated humidifiers may mitigate such noncompliance; however, recent observations suggest that their use, particularly if not cleaned, increases the risk of respiratory infections. Humidifier water may be contaminated, but the long-held view that passive humidifiers cannot aerosolize water may obscure the perception of risk of infection.

OBJECTIVES

This study challenges the long-held view that "passover" humidifiers do not aerosolize water. With such evidence, this study characterizes the performance of filters to reduce the potential risk of contamination.

METHODS

Heated humidifier water contaminated with bacteria was studied under conditions simulating week-long use of nCPAP for OSA.

RESULTS

Bacteria were recovered in 9 of 11 tests from the breathing tubes of CPAP devices fitted with heated humidifiers with water contaminated with Brevundimonas diminuta or Serratia marcescens. Recoverable bacteria ranged from tens to thousands of colony forming units when tested at air flow rates of 60 liters per minute for 90 minutes. Neither organism was recovered from the circuit tubing when a hydrophobic breathing-circuit filter was positioned between the humidifier and face-mask tubing with a commercially available nCPAP machine tested under simulated-use conditions.

CONCLUSION

Data suggest that patients with OSA being treated with nCPAP fitted with humidifiers may be aerosolizing bacteria, putting them at risk for developing respiratory infections and that the use of a hydrophobic filter may attenuate the passage of microbes from contaminated humidifier water.

Day care in relation to respiratory-tract and gastrointestinal infections in a German birth cohort study

AIM

To describe day care attendance in Germany today (in former East and former West Germany). To investigate longitudinally whether children attending day care centres have an increased risk of acquiring common cold, bronchitis, pneumonia, otitis media or diarrhea.

METHODS

Questionnaire information was collected when the children in the cohort were 6, 12, 18, 24 months, and 4 and 6 years old. Day care within the first and first 2 years of life was investigated longitudinally with GEE (generalised estimating equations) methods in relation to common cold, bronchitis, pneumonia, otitis media and diarrhea within the first 6 years of life.

RESULTS

Day care centre attendance is more common in former East than in former West Germany; this difference is evident even 10-12 years after German reunification. Children attending a day care centre were more likely to have common cold, bronchitis, pneumonia, otitis media and diarrhea within the first 2-3 years of life. With the exception of common cold, from year 4 onwards these associations were not statistically significant anymore and even reversed for some of the infections.

CONCLUSIONS

Children attending day care centres were at an increased risk of respiratory and gastrointestinal infections within the first years of life. However, around school age these differences disappeared or even partly reversed.