New knol on Modeling the critical care demand and antibiotics resources needed during the Fall 2009 wave of influenza A(H1N1) pandemic

We recently published a knol in PLoS Currents Influenza about the estimate of the demand for critical care and antibiotic usage due to the Fall 2009 wave of pandemic Influenza H1N1.

Modeling the critical care demand and antibiotics resources needed during the Fall 2009 wave of influenza A(H1N1) pandemic
D Balcan, V Colizza, AC Singer, C Chouaid, H Hu, B Gonçalves, P Bajardi, C Poletto, JJ Ramasco, N Perra, M Tizzoni, D Paolotti, W Van den Broeck, A-J Valleron and A Vespignani.
PLoS Currents: Influenza.
2009 Dec 4, RRN1133.

The most common symptoms of influenza are generally mild for the majority of people infected. However, in a small portion of clinical cases infected with influenza, the disease can lead to complications of increasing severity requiring medical attention, antibiotics, and, in more serious situations, hospitalization and intensive care. Given the limited capacity of health care providers and hospitals and the limited supplies of antibiotics, it is important to predict the potential demand on critical care to assist planning for the management of resources and plan for additional stockpiling.

In the knol, we introduce a model that considers the development of influenza-associated complications and incorporate it into a GLEaM to assess the expected surge in critical care demands due to viral and bacterial pneumonia. More specifically, the new compartmentalization adds to the basic structure of the influenza dynamics a set of compartments and transitions taking into account the possible evolution of the complications associated to an influenza infection, including viral and bacterial pneumonia, and different speed of progression and stages of severity of the disease. It includes home treatment, hospitalizations, and admission to intensive care unit (ICU). Patients in each stage of pneumonia complications are assumed to be treated with antibiotics, with a preferred empirical antibiotic regimens based on the guidelines issued by the British Thoracic Society. A sketch of the complete compartmental model can be seen in the figure below (click on the left panel to zoom in).

Sketch of the compartment relations for the new epidemic model

Sketch of the compartment relations for the new epidemic model

figure2_knol

Time evolution of the ICU occupancy in a set of countries, measured as the predicted need of ICU beds per 100,000 persons.

Based on the most recent estimates of complication rates, we predict the expected peak number of intensive care unit beds and the stockpile of antibiotic courses needed for the current pandemic wave. The effects of dynamic vaccination campaigns (see this post), and of different length of staying in the intensive care unit are also explored. The right panel of the figure (click on it to expand it) shows the predicted ICU occupancy as a function of time for four countries of the Northern Hemisphere. The three profiles per each country refer to the predicted ICU occupancy in the baseline case when no intervention is implemented, and in case dynamic vaccination campaigns with distribution rates rv=0.1% and rv=1% are considered. Solid curves correspond to the median profiles and the shaded areas to the 95% reference range obtained from 2,000 stochastic simulations. The average ICU length of staying is assumed equal to 7 days.

Tables 1 displays further details on these ICU predictions for a baseline situation and when a vaccination campaign with distribution rates rv=0.1% is considered. The predicted need of ICU beds at peak are typically moderate even when the baseline scenario without intervention is considered, ranging approximately from 5 to 7 ICU beds per 100 000 inhabitants, well below the average national capacity of ICU beds per 100,000 inhabitants. Such numbers can be reduced if measures as vaccination campaigns are taken into account.

ICU occupancy at peak (per 100,000)
Country
Vaccination campaign 0.1% population/day
7 days
10 days
14 days
US
[5.0-5.5]
[6.7-7.3]
[8.6-9.4]
UK
[5.5-6.2]
[7.4-8.2]
[9.6-10.5]
Canada
[4.8-5.5]
[6.5-7.3]
[8.5-9.5]
France
[5.7-6.2]
[7.6-8.3]
[9.8-10.6]
Italy
[6.2-6.7]
[8.2-8.9]
[10.5-11.3]
Spain
[5.6-6.1]
[7.5-8.2]
[9.6-10.5]
Germany
[6.4-7.0]
[8.5-9.2]
[10.8-11.6]

Table 1: Predicted need of ICU beds in a scenario with a vaccination campaign covering 0.1% of the population per day until end of vaccine stockpile. The 95% reference range (RR) of the daily number of occupied ICU beds per 100,000 is reported at its peak for several countries in the Northern Hemisphere.

Table 2 reports the number of antibiotics courses needed daily at the peak of the requests, and the total size predicted to be used at the end of the pandemic wave, based on the empirical guidelines of the British Thoracic Society and broken down by the stage of severity of pneumonia. A single course of antibiotics is defined as the combination of antimicrobial drugs considered in the treatment regimen for the suggested duration (see the knol for additional details). The total size of antibiotics courses predicted to be used in the current Fall 2009 pandemic is in the range of [6,337-7,149] per 100,000 for the set of countries explored, which needs to be compared with the available stockpiles of antibiotics courses to cover high-risk groups. Many countries however do not possess nation-wide antibiotic supplies, as antibiotics are generally available through short supply chains able to fulfill average just-in-time requests. The estimates contained in Table 2 can therefore be considered as guidelines to assess the expected needs during the remaining evolution of the pandemic wave with respect to the present usage pattern and available resources.

Antibiotic usage – vaccination with rv=0.1%
Country
Daily administered AB courses at peak (per 100,000)
Total administered AB courses at the end of pandemic wave (per 100,000)
Pneumonia
stage I
Pneumonia
stage II
Pneumonia
stage III
Pneumonia
stage I
Pneumonia
stage II
Pneumonia
stage III
US
[151-166]
[4.4-4.8]
[0.8-0.9]
[6,005-6,220]
[177-184]
[30.7-31.9]
UK
[170-186]
[4.9-5.4]
[0.9-1.0]
[6,297-6,540]
[186-193]
[32.1-33.6]
Canada
[147-164]
[4.3-4.9]
[0.8-0.9]
[6,278-6,457]
[185-191]
[31.8-33.3]
France
[176-188]
[5.1-5.5]
[0.9-1.0]
[6,357-6,585]
[188-195]
[32.3-33.8]
Italy
[191-206]
[5.5-6.0]
[1.0-1.1]
[6,481-6,633]
[191-196]
[32.9-34.1]
Spain
[171-185]
[5.0-5.4]
[0.9-1.0]
[6,335-6,511]
[187-193]
[32.1-33.6]
Germany
[200-216]
[5.7-6.2]
[1.0-1.2]
[6,476-6,654]
[191-197]
[33.0-34.2]

Table 2: Predicted usage pattern of antibiotics in the scenario with the previous vaccination campaign. The 95% RR of the daily number of administered antibiotics courses per 100,000 at its peak is reported, along with the total amount predicted to be administered by the end of the pandemic wave. Results are shown for several countries in the Northern Hemisphere, broken down for different stages of influenza-associated complications. Pneumonia stages I, II and III corresponds to home-treatment (or supervised outpatient treatment), hospital wards and ICU, respectively.

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