Relative contributions of four exposure pathways to influenza infection risk

[mixin]

The relative contribution of four influenza virus exposure pathways must be quantified to determine the potential efficacy of nonpharmaceutical interventions of transmission.:
(1) virus-contaminated hand contact with facial membranes
(2) inhalation of respirable cough particles
(3) inhalation of inspirable cough particles
(4) spray of cough droplets onto facial membranes

We used a mathematical model to estimate the relative contributions of the four pathways to infection risk in the context of a person attending a bed-ridden family member ill with influenza. Considering the uncertainties in the sparse human subject influenza dose-response data, we assumed alternative ratios of 3,200:1 and 1:1 for the infectivity of inhaled respirable virus to intranasally instilled virus.

For the 3,200:1 ratio, pathways (1), (2), and (4) contribute substantially to influenza risk: at a virus saliva concentration of 10(6) mL(-1), pathways (1), (2), (3), and (4) contribute, respectively, 31%, 17%, 0.52%, and 52% of the infection risk. With increasing virus concentrations, pathway (2) increases in importance, while pathway (4) decreases in importance.

In contrast, for the 1:1 infectivity ratio, pathway (1) is the most important overall: at a virus saliva concentration of 10(6) mL(-1), pathways (1), (2), (3), and (4) contribute, respectively, 93%, 0.037%, 3.3%, and 3.7% of the infection risk. With increasing virus concentrations, pathway (3) increases in importance, while pathway (4) decreases in importance.

Given the sparse knowledge concerning influenza dose and infectivity via different exposure pathways, nonpharmaceutical interventions for influenza should simultaneously address potential exposure via hand contact to the face, inhalation, and droplet spray.

Nicas M, Jones RM

http://www.ncbi.nlm.nih.gov/pubmed/19558389?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum

[gsgs]

Re: Relative contributions of four exposure pathways to influenza infection risk

thanks.

full article here:

http://www3.interscience.wiley.com/cgi-bin/fulltext/122466317/HTMLSTART

American paper, so the "," is not a decimal point so "3,200" is presumably 3200

so, what are the % of the 4 transmissions ?


trying to figure it out....


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facial membranes, I assume that's
a) nose (inside the nose hole, sticking a finger into the nose)
b) eye (contaminating some eye-liquid with a finger, which then goes back into the eye)
c) lips (touching a lip with a finger)
d) mouth,tongue,gums,throat (eating,drinking,finger)
e) ear (touching with a finger or contaminated Q-tips)

presumably only a)nose occurs with normal human flu

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in 1) they say "hand-contact" but any other contact is presumably included, e.g. eating,kissing
in 2),3),4) they say "cough-particles" but presumably speak-particles and sneeze-particles are included

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they give:

1) eyes, nostrils, and lips
2) particles <10 micron
3) particles 10-100 micron
4) >100 micron

inspirable: head airways, tracheobronchial only

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[mixin]

Re: Relative contributions of four exposure pathways to influenza infection risk

I re-did the the comparisons to read easier:

For the 3,200:1 ratio
(1) virus-contaminated hand contact with facial membranes 31%
(2) inhalation of respirable cough particles 17%
(3) inhalation of inspirable cough particles 0.52%
(4) spray of cough droplets onto facial membranes 52%

the 1:1 infectivity ratio
(1) virus-contaminated hand contact with facial membranes 93%
(2) inhalation of respirable cough particles 0.037%
(3) inhalation of inspirable cough particles 3.3%
(4) spray of cough droplets onto facial membranes 3.7%

[gsgs]

Re: Relative contributions of four exposure pathways to influenza infection risk

what I estimate that they estimate is:

60% of flu-infection occurs by hands touching eyes,nostrils,lips
10% of flu-infection occurs by inhaling small airborn particles
20% of flu-infection occurs by inhaling large particles >0.1mm

[mixin]

Re: Relative contributions of four exposure pathways to influenza infection risk

But if we have a 1:1 infectivity ratio, then by hands goes up to 93%.

We don't know a lot about infectivity; do we have a 1:1 ratio often?

That receptors for human-origin influenza A are located throughout the respiratory tract (from the nasal mucosa to the bronchioles) suggests that all exposure pathways may be relevant.(12,13) However, the apparent absence of receptors in oral and ocular tissues implies that virus deposited in these regions must be transported to nasopharyngeal tissues to initiate infection.

Receptors for avian-origin influenza A are localized in the terminal bronchioles, alveoli, corneal and ocular conjunctive tissue, and occasionally in the nasal mucosa; these locations suggest that respirable particle inhalation may be the more important pathway.(13,14) Concordance of the receptor locations with viral binding sites has been confirmed in human bronchiole and alveolar tissues.(13,15)

[gsgs]

Re: Relative contributions of four exposure pathways to influenza infection risk

they consider 1:1 and 3200:1 . They must have some reason for this.
What else can I do than assume both are equally likely and
others don't occur ?

By refining this you may come to better estimates, but so far
I think what I gave is the best available.

Hopefully this motivates others to do research their own estimates,
trying to "refute" these ones ....
(to my experience that's a strong motivation ;-) )
So thanks to Nicas and Jones to get this started.


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hold your breath while eating/drinking potentially flu-contaminated things

[gsgs]

Re: Relative contributions of four exposure pathways to influenza infection risk

Clinical Infectious Diseases 2010;50:000?000? 2010 by the Infectious Diseases Society of America. All rights reserved.
1058-4838/2010/5005-00XX$15.00
DOI: 10.1086/650457


Clin Infect Dis. 2010 Jan 25. [Epub ahead of print]

Distribution of Airborne Influenza Virus and Respiratory Syncytial Virus in an Urgent Care Medical Clinic.
Lindsley WG, Blachere FM, Davis KA, Pearce TA, Fisher MA, Khakoo R, Davis SM, Rogers ME, Thewlis RE, Posada JA, Redrow JB, Celik IB, Chen BT, Beezhold DH.

Health Effects Laboratory Division and 2Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, and Departments of 3Medicine, 4Emergency Medicine, and 5Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia.

Background. Considerable controversy exists with regard to whether influenza virus and respiratory syncytial virus (RSV) are spread by the inhalation of infectious airborne particles and about the importance of this route, compared with droplet or contact transmission. Methods. Airborne particles were collected in an urgent care clinic with use of stationary and personal aerosol samplers. The amounts of airborne influenza A, influenza B, and RSV RNA were determined using real-time quantitative polymerase chain reaction. Health care workers and patients participating in the study were tested for influenza. Results. Seventeen percent of the stationary samplers contained influenza A RNA, 1% contained influenza B RNA, and 32% contained RSV RNA. Nineteen percent of the personal samplers contained influenza A RNA, none contained influenza B RNA, and 38% contained RSV RNA. The number of samplers containing influenza RNA correlated well with the number and location of patients with influenza ([Formula: see text]). Forty-two percent of the influenza A RNA was in particles 4.1 mum in aerodynamic diameter, and 9% of the RSV RNA was in particles 4.1 mum. Conclusions. Airborne particles containing influenza and RSV RNA were detected throughout a health care facility. The particles were small enough to remain airborne for an extended time and to be inhaled deeply into the respiratory tract. These results support the possibility that influenza and RSV can be transmitted by the airborne route and suggest that further investigation of the potential of these particles to transmit infection is warranted.

PMID: 20100093 [PubMed - as supplied by publisher]

http://www.journals.uchicago.edu/doi/abs/10.1086/650457