Estimation of Needed Isolation Capacity for an Airborne Influenza Pandemic

Abstract

We estimated the number of isolation beds needed to care for a surge in patients during an airborne-transmissible influenza pandemic. Based on US health system data, the amount of available airborne isolation beds needed for ill patients will be exceeded early in the course of a moderate or severe influenza pandemic, requiring medical facilities to find ways to further expand isolation bed capacity. Rather than building large numbers of permanent airborne infection isolation rooms to increase surge capacity, an investment that would come at great financial cost, it may be more prudent to prepare for wide-scale creation of just-in-time temporary negative-pressure wards.

The authors estimated the number of isolation beds needed to care for a surge in patients during an airborne-transmissible influenza pandemic. Based on US health system data, the number of available airborne isolation beds needed for ill patients will be exceeded early in the course of a moderate or severe influenza pandemic, requiring medical facilities to find ways to further expand isolation bed capacity. It may be prudent to prepare for wide-scale creation of just-in-time temporary negative-pressure wards.

An influenza pandemic that can spread from person to person by airborne transmission poses unique containment challenges. Engineering infection control measures—namely, facility airflow management—will play a key role in where ill patients are hospitalized. While North American hospitals have substantial experience responding to outbreaks of seasonal influenza, which is believed to be spread primarily via droplet transmission, few have experience caring for large numbers of patients with infections that are primarily airborne transmissible. The most recent germane example may be the outbreak of severe acute respiratory syndrome (SARS) in 2003, in which Canadian healthcare facilities rapidly built airborne isolation units that allowed them to safely care for a large number of SARS patients.¹ The rapid build-up of airborne isolation capacity was a key component in the successful containment of this outbreak, which up to that point had been transmitted mostly in healthcare facilities.^2,3

Public health agencies, professional societies, and infection control experts emphasize the importance of stringent hospital infection prevention measures to help prevent airborne transmission,^4,5 including the capacity to isolate patients in spaces with directional airflow; yet healthcare facilities are sometimes inadvertent nodes of transmission.^6,7 While airborne infection isolation rooms (AIIR) are widely used in US hospitals for patients with suspected or confirmed airborne-transmissible diseases, the numbers or locations of these rooms are generally not regulated. The US Centers for Disease Control and Prevention (CDC) recommends that each hospital or health system perform a risk assessment to make decisions about availability of airborne isolation space, based in part on the community-level burden of tuberculosis.⁸ Given the low incidence of tuberculosis in the United States, the number of airborne infection isolation beds is generally low.

According to a 2003 congressional report, around 66% of urban US hospitals have fewer than 5 isolation beds per 100 staffed beds, and only 9.5% have 10 or more isolation beds per 100 staffed beds.⁹ Another study conducted in 1993 evaluated several Midwestern hospitals for respiratory isolation and reported only 3.4% of the hospital rooms were designed to have negative pressure ventilation suitable for respiratory isolation.¹⁰

More recently, concerns have been raised about the capacity of the US healthcare system to accommodate a surge of infectious patients during an influenza pandemic or another large-scale airborne infectious disease outbreak,^11,12 especially given the uncertain risks of emerging and re-emerging infectious disease outbreaks.¹³ How many airborne isolation beds would be needed across the United States for a large-scale outbreak? We sought to understand the quantity of airborne isolation rooms needed to house a surge of infectious patients during an influenza pandemic, benchmark it against estimates of existing airborne infection isolation rooms, and discuss options to create surge airborne isolation bed space in the event of an outbreak.

Methods

Estimating Airborne Isolation Needs

We estimated the total number of hospitalizations and deaths for a mild, moderate, or severe pandemic and used these values as inputs to the CDC's FluSurge 2.0 pandemic modeling tool to quantify the number of people who might need airborne isolation.¹⁴ Estimated hospitalizations and deaths during a mild pandemic were obtained from the published burden of the 2009 H1N1 pandemic influenza (for a population of approximately 309 million in 2010) in the United States, as shown in Table 1.^15,16 The expected hospitalizations and deaths during a moderate or severe influenza pandemic were derived from the Department of Health and Human Services (HHS) pandemic planning assumptions as follows: (1) a clinical attack rate of 30%; (2) probability of ill patients seeking healthcare of 50%; (3) hospitalization rate of 22% of those seeking care during a severe pandemic and 2% during a moderate pandemic; (4) case fatality rate of 2.1% for ill patients during a severe pandemic and 0.23% for a moderate pandemic; and (5) a pandemic wave duration of 8 weeks.¹⁷

Table 1.

Clinical Impact and Healthcare Use of a Sample Population of 10,000 during Mild, Moderate, and Severe Pandemics

	Mild Pandemic	Moderate Pandemic	Severe Pandemic
Population	10,000
No. people falling sick	N/A	3,000
No. seeking health care	N/A	1,500
Total hospitalizations	8.88^*	30	330
Deaths	0.4^*	7	63
Average weekly census
Week 1	0.5	1.6	17.5
Week 2	0.8	2.8	30.6
Week 3	1.2	4.2	46.1
Week 4	1.6	5.4	58.9
Week 5 (Peak)	1.7	5.6	61.5
Week 6	1.5	5	55.4
Week 7	1.2	3.9	42.9
Week 8	0.8	2.6	28.5

Estimated using US 2009 H1N1 pandemic influenza data in the United States.¹⁴

N/A = Not available.

The resulting number of hospitalizations and deaths were entered into the custom fields of FluSurge 2.0 to calculate the average number of hospitalized patients during each pandemic week for each of the 3 different pandemic intensities.¹⁴ ICU and non-ICU occupancy outputs from FluSurge were added to determine the total number of infectious patients expected each week, assuming a population of 10,000 people (Table 1). It was assumed that all the infectious patients would need to be placed on airborne infectious isolation precautions and each airborne infection isolation room would house 1 patient (or bed) only, since most airborne infection isolation rooms are designed as single patient rooms.

Comparing Estimates of Needed and Available Beds

Using publicly available national and state-level data,^9,18 we compared our estimates of needed airborne isolation beds during mild, moderate, and severe pandemics to airborne infection isolation room availability. The national survey included ranges of AIIR per 100 staffed beds of 1,482 hospitals.⁹ We considered the midpoint of each of these ranges and the corresponding number of hospitals for each range and calculated a weighted average of 4.64 AIIR per 100 staffed beds. This was converted to AIIR/10,000 persons using the Organisation for Economic Co-operation and Development's estimate of 29 hospital beds (for 2013) per 10,000 persons for the United States.¹⁹

Similarly, survey data for the state of Massachussetts¹⁸ was available as mean AIIR for a range of hospital sizes (defined as number of beds). The corresponding number of hospitals was also available for each of these ranges. The weighted average of 6.78 AIIR per 100 staffed hospital beds was calculated considering the midpoint of the hospital size ranges, the mean AIIR for each range, and the number of hospitals in each range. This was converted to AIIR/10,000 persons in Massachusetts using the Kaiser Family Foundation's estimate of 25 hospital beds (for 2013) per 10,000 persons.²⁰

We also compared the estimated AIIR needs to existing AIIR capacity in VA medical facilities and adjusted this number to AIIR per 10,000 enrollees (unpublished data). Lastly, the CDC-recommended minimum of 1 AIIR per 120 beds⁸ was converted to AIIR per 10,000 persons.¹⁹

Results

The estimated number of affected individuals, hospitalizations, deaths, and average census of patients during each week of the modeled pandemic 8-week wave for a population of 10,000 persons are shown in Table 1. Using this model, the AIIR demands increase on a weekly basis and peak during week 5 at 1.7/10,000 for a mild pandemic, 5.6/10,000 for a moderate pandemic, and 61.5/10,000 for a severe pandemic, decreasing gradually afterwards for all 3 pandemic severities. Figure 1 compares calculated AIIR availability to estimated AIIR needs per 10,000 persons for a mild, moderate or severe influenza pandemic. The average existing AIIR per 10,000 persons, calculated from the national and state surveys, are 1.35 and 1.70, respectively. VA facilities have an average of 2.7 AIIRs per 10,000 persons. All these values are above the minimum CDC-recommended AIIR capacity of 0.24 AIIR/10,000 persons.

Figure 1.

AIIR Need Estimates for Mild, Moderate, or Severe Pandemic Scenarios with an 8-Week Wave Duration

Discussion

Our study provides estimates for airborne infection isolation room demand based on modeled pandemic scenarios. These estimates provide a point of reference for pandemic planning but are not meant to be exact predictors of the impact of the next influenza pandemic. The larger issue this study addresses is that surge isolation capacity must be a component of pandemic planning in healthcare facilities.

Based on our analysis, the amount of available airborne isolation beds (or AIIRs), on a national or state scale, would likely be sufficient to accommodate the number of ill patients expected during a mild influenza pandemic; however, the surge expected during a moderate or severe airborne-transmissible influenza pandemic would exceed available airborne isolation capacity early in the outbreak.

While generally not regulated, the number of airborne isolation beds in US healthcare facilities is at least partly based on perceived risks of airborne infectious disease outbreaks in each community, including recent hospitalizations for infections caused by Mycobacterium tuberculosis.⁸ Due in part to the relatively low incidence of tuberculosis in most US communities during the past 2 decades, the number of airborne isolation beds in hospitals is typically small.

If the current number of airborne isolation beds is too low, what quantity would be sufficient during an influenza pandemic? According to our analysis, during a moderate pandemic, approximately 6 isolation beds per 10,000 persons in the catchment community would be necessary, a 4-fold increase from current AIIR availability; and for a severe pandemic it would be substantially higher—approximately 62 isolation beds (a 45-fold increase from current AIIR availability) per 10,000 persons.

Additional airborne isolation bed space, needed to house a surge of ill patients, may be created by at least 4 methods (Table 2): (1) new permanent construction, (2) retrofitting an existing patient room with a temporary configuration as individual AIIR, (3) converting an existing hospital ward into a temporary airborne infection isolation ward, or (4) creating additional AIIR beds in non–patient care spaces. As noted in the table, building new permanent AIIR is the most expensive option, costing approximately $80,000 to $100,000 (in 2015 US dollars) per AIIR.^21,22 At this cost level, a facility with 300 beds (and approximately 14 AIIRs) would need to invest between $3.4 and $4.2 million to build an additional 42 AIIR beds to meet the projected demand in a moderate pandemic. On a national scale (for the US population of approximately 320 million in 2015) to build permanent AIIRs to meet the projected demand of a moderate severity airborne-transmissible pandemic would cost $11.8 to $14.7 billion.²³

Table 2.

Options for Creating Additional Airborne Isolation Surge Space

Option	Pros	Cons	Cost
Permanent construction of individual AIIRs²¹	Meet CDC and AIA guidelines	• High cost • Low routine incidence of diseases requiring isolation limits utility	• $40,000-$50,000 in 1988 dollars²¹ ($80,000-$100,000 in 2015 dollars)
Retrofitting nonisolation hospital room for 1 or 2 patients temporarily²⁸	• Can be set up relatively quickly if plans are pre-developed • Provides access to medical utilities and clinical infrastructure • Can maintain individual isolation	• Creates AIIR surge capacity at the expense of routine hospital bed space • Installation may create challenges for clinical care	• Less than $2,300²⁸ for an individual room
Conversion of existing patient units/wards to isolation wards^25,26	• Can be set up relatively quickly if plans are pre-developed • Provides access to medical utilities and clinical infrastructure • Can provide a significant increase in AIIRs	• Creates AIIR surge capacity at the expense of routine hospital bed space • Installation may create challenges for clinical care	• Data not available on ward conversion
Retrofitting large existing general hospital space (physical therapy gymnasium) temporarily^21,27	• Can be set up relatively quickly if pre-planned and pre-developed • Creates significant number of negative pressure isolation beds	• Potential for unknown infectious aerosol distribution and exposure in large areas • Limited utilities (medical gas, suction, power) are barrier to higher acuity care	• Less than $6,000 (including personnel, HEPA units, ventilation, and engineering/construction costs²¹)

Assuming this level of investment is cost prohibitive for spaces that will be infrequently or rarely used,¹¹ creation of temporary isolation spaces as needed during an event may be favored, similar to the negative pressure isolation wards built in Hong Kong, Taiwan, and Toronto during the SARS crisis.^2,24 In Taiwan, for example, patients were grouped in private rooms on dedicated SARS wards that were reengineered and their ventilation systems modified to separate the ward from the rest of the hospital.²

In Toronto, early in the SARS outbreak, the available negative pressure rooms in most hospitals were full and additional patients were waiting in emergency departments and homes to be treated. In response, the Ontario government declared a provincial emergency and required all hospitals to create their own SARS units.¹ The York Central hospital set up a 15-bed SARS assessment and treatment unit (SATU) within 24 hours on a previously empty ward equipped with a ventilation system and isolated from the rest of the hospital. The unit was maintained at negative pressure relative to the hospital by means of externally vented exhaust fans, and private rooms on the unit were kept at negative pressure relative to the corridor with the help of externally exhausted high-efficiency particulate aerosol (HEPA) filters.²⁵ The North York General Hospital in Toronto had 46 patients in respiratory isolation at the peak of the SARS II outbreak. This was possible because 2 units were converted into SARS wards (with a total of 49 rooms) within 72 hours of the outbreak.²⁶

As noted in Table 2, while the temporary approaches to creating surge spaces in nonclinical areas are feasible, it may be challenging to equip these spaces with the same utilities, such as medical gases, suction, and power, as a built hospital room,²⁷ potentially limiting the level of care that can be provided in the available space. In Toronto, both hospitals used existing patient-care space containing appropriate clinical resources and utilities.

An important factor to consider is the rapidity with which additional airborne isolation bed space may need to be implemented. During a moderate or a severe pandemic, airborne isolation beds may be insufficient in most institutions after only a few days. Since local and regional heterogeneity in the severity of a pandemic is unpredictable, all localities have to consider the possibility that their capacity may be overwhelmed rapidly and plan accordingly. Facilities should consider that there is a baseline demand and occupancy of airborne infection isolation rooms in health care, so that some of the existing capacity may already be unavailable. Therefore, having pre-established plans is paramount. Hospitals should take certain steps to prepare to increase airborne isolation bed space in the event of an airborne infectious disease outbreak^11,26:

• Make an assessment of the facilities' current capabilities;

• Make sure the facilities' most current blueprints are readily available and accessible if needed to make necessary changes;

• Work in a multidisciplinary team with hospital leadership, engineering, and clinical staff to plan for creation of adequate negative-pressure space;

• Identify potential areas that can be converted effectively with minimum modifications; and

• Define engineering, administrative, and personnel requirements and build out space that can be efficiently implemented during an event.

While these recommendations are important to develop viable surge capacity plans, they lack guidance about the amount of capacity to be built. Our analysis suggests a planning target of 6 isolation beds/10,000 persons in the hospital's catchment population would significantly improve capability for a moderate influenza pandemic. Temporary conversion of existing patient beds to an AIIR configuration, either individually or as wards, provides for complex clinical care of seriously ill patients in a negative pressure isolation environment, but requires significant planning with a multidisciplinary team to be able to implement efficiently during an event.

Limitations of this analysis should be taken into consideration when interpreting the results. Our observations are based on a model and are not experiential. Each influenza pandemic is unique in severity and transmissibility. The exact characteristics of the next pandemic are therefore impossible to predict. We used standard pandemic planning assumptions published by HHS to create potential scenarios, with the understanding that the next pandemic may be dissimilar from previous ones and may not fit within FluSurge parameters. Some of the survey data, used for comparison with the model, although the best and most recent we could find in the public domain, are 10 to 12 years old. The expected hospitalizations and deaths during moderate and severe pandemics, used as input for the model, are estimates based on extrapolations of pandemics from the 20th century. They do not take into account the impact of interventions available in the 21st century,¹⁷ nor do they account for the impact on pandemic epidemiology of contemporary global connectivity.

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