1.1. Acute respiratory infections in health care
Acute respiratory infections (ARIs) are the leading cause of morbidity and mortality from infectious disease in the world. Almost four million people die from ARIs each year, with 98% of these deaths due to lower respiratory tract infections. Mortality rates are particularly high in infants, children, and the elderly, particularly in low-income and middle-income countries (19, 20). ARIs are one of the most frequent causes of consultation or admission to health-care facilities, particularly in paediatric services (21).
Bacteria are a major cause of lower respiratory tract infection, with Streptococcus pneumoniae being the most common cause of bacterial community-acquired pneumonia in many countries. However, the pathogens that most often cause ARIs are viruses or mixed viral–bacterial infections. ARIs that have epidemic or pandemic potential, and may pose a public-health risk, warrant special precautions and preparedness (22).
The incidence of specific ARIs, their distribution and the outcome of disease varies according to several factors, including (23-25):
environmental conditions (e.g. air pollutants, household crowding, humidity, hygiene, season and temperature);
availability and effectiveness of medical care and
infection prevention and control (IPC) measures to contain spread such as vaccines, access to health-care facilities, and isolation capacity;
host factors such as age, cigarette-smoking, host ability to transmit infection, immune status, nutritional status, prior or concurrent infection with other pathogens, and underlying medical conditions; and
pathogenic characteristics, including modes of transmission, transmissibility, virulence factors (e.g. genes encoding toxins) and microbial load (inoculum size).
1.2. Scope of the current guidelines
This document provides recommendations and other information relating to IPC measures for ARIs in health-care settings, with specific emphasis on ARIs that have the potential for rapid spread and may cause epidemics or pandemics (or both). Some of the epidemic-prone ARIs may constitute a global public-health emergency. According to the International Health Regulations (IHR), 2005 (6) the respiratory disease events that may constitute a public-health emergency of international concern include:
severe acute respiratory syndrome (SARS);
human influenza caused by a new subtype, including human episodes of avian influenza;
pneumonic plague; and
novel ARIs that can cause large-scale outbreaks, or outbreaks with high morbidity and mortality.
Recommendations for prevention and control of pneumonic plague have been addressed in a previous World Health Organization (WHO) publication Operational guidelines on plague surveillance, diagnosis, prevention and control, 2009 (26), and a summary of IPC precautions is provided in Table 2.1 in these guidelines.
Tuberculosis (TB) seldom presents as an ARI. However, its spread has been associated with health care and is a major global health concern. Recommendations for prevention and control of TB in health-care facilities have been addressed in a previous WHO publication – WHO policy on TB infection control in health-care facilities, congregate settings and households, 2009 (27) – and a summary of IPC precautions is provided in the Table 2.1.
This document focuses on the most common ARIs, and highlights ARIs of potential concern. In particular, these guidelines address IPC precautions for ARIs that:
cause acute respiratory tract infection, including pneumonia and acute respiratory distress syndrome;
cause severe disease in susceptible people with apparently normal immune systems; and
may constitute a public health emergency of international concern as defined by IHR (
6), except in the case of pneumonic plague.
1.3. ARIs that may constitute a public health emergency of international concern covered in the current document
1.3.1. Severe acute respiratory syndrome
SARS is caused by the SARS coronavirus (SARS-CoV) (28) that can infect animals and humans. The disease was first reported in Asia in February 2003, and spread to people in over 24 countries in Asia, Europe, North America and South America before the outbreak was contained (29). SARS is currently not known to be circulating among people, but it could still be circulating in animal hosts and may thus re-emerge in humans (30). Human-to-human transmission of SARS occurs mainly through droplets or direct contact, although transmission through infectious respiratory aerosols of various sizes may occur at short range (31).
1.3.2. New influenza virus causing human infection
Influenza viruses can infect many species, including humans, birds, pigs, horses and seals. Birds, in particular, are the main reservoir for influenza A viruses. Influenza viruses tend to infect people sporadically or in seasonal epidemics; occasionally, when a new human influenza virus emerges, it can cause a worldwide pandemic. Seasonal epidemics are caused by influenza viruses that are well adapted to the human hosts they circulate in. When an influenza virus with the capacity to infect humans first emerges in another species, it is not yet adapted to humans and may circulate in animal hosts, generating sporadic human infections. Because it may subsequently evolve the ability for sustained human-to-human transmission, any new influenza virus that generates sporadic cases of human infection may present a pandemic risk. Thus, early detection, isolation and warning of sporadic infections are crucial to minimize the risk of serious public health impacts from new influenza viruses (32).
Direct transmission of avian influenza viruses – including H5N1, H7N9, H7N2 and H9N2 – to humans has been described on numerous occasions (33-36), and often results in a high fatality rate (37). The most important avian virus infecting humans in recent years has been avian influenza A(H5N1), which can be highly pathogenic. Human cases of H5N1 were reported in Hong Kong Special Administrative Region (SAR), China, in 1997, and have been found in other countries since 2003. Because A(H5N1) is believed to be circulating widely among wild birds, more cases in people are expected. Most instances of avian influenza infection in people have resulted from contact with infected poultry (e.g. domesticated chickens, ducks or turkeys) or surfaces contaminated with secretions or excretions from infected birds (33-40). So far, however, no efficient or sustained human-to-human transmission of avian influenza A(H5N1) has been demonstrated. In the potential cases of human-to-human transmission, infection was associated with close, extensive unprotected contact, suggesting that the virus might have spread through respiratory droplets or contact (37, 41).
Pandemic influenza A (H1N1) 2009 virus resulted from genetic re-assortment of swine, avian and human viruses, and it is efficiently spread through human-to-human transmission (42). First recognized in North America in April 2009, A(H1N1)pdm09 subsequently spread around the globe, causing a pandemic between June 2009 until August 2010 (43, 44).
1.3.3. Novel acute respiratory infections with potential for a high public health impact
Infectious diseases have spread across populations and regions throughout history, and it is likely that newly emerging infectious diseases will continue to be identified. Many infectious diseases with animal reservoirs can sometimes infect humans. Two examples that occurred after the 2009 influenza pandemic are human cases of influenza A(H7N9) which first occurred in 2013, and of Middle East Respiratory Syndrome (MERS) coronavirus from 20121.
The following factors have been associated with the emergence and spread of infectious diseases (22, 45):
changes in human demographics and behaviour;
impact of new technologies and industries;
economic development and changes in land use;
increased international travel and commerce;
microbial adaptation and change;
poor implementation of public-health measures; and
sharing an environment with domestic or wild animals, including birds.
When a new infectious disease is identified, the modes of transmission are not well understood. The epidemiological and microbiological studies needed to determine the modes of transmission and identify possible IPC measures may be protracted. Due to the lack of information on modes of spread, Airborne and Contact Precautions, as well as eye protection, should be added to the routine Standard Precautions whenever possible, to reduce the risk of transmission of a newly emerging agent (Annex B describes Standard and other precautions). These precautions should be implemented until further studies reveal the mode of transmission. Epidemiological and clinical clues can indicate when additional precautions are needed (Section 2.1).
It is essential to maintain close surveillance of health-care workers from the very beginning of an outbreak with a novel pathogen, and during the outbreak, since this could offer important information about means of transmission, both for community and health-care associated transmission.
1.4. Infection prevention and control guiding principles
The conditions and levels of complexity in health-care facilities vary within and between countries. Policy-makers and health administrators should identify strategies with optimal cost-effectiveness ratios based on the facilities' potential for sustainable and continuous quality improvement.
The principles of IPC for ARI patient care include:
early and rapid recognition of patients;
application of routine IPC precautions (Standard Precautions) for all patients;
additional precautions in selected patients (e.g. based on the presumptive diagnosis);
IPC strategies in health-care facilities are commonly based on early recognition and source control, administrative controls, environmental and engineering controls, and personal protective equipment (PPE).
1.4.1. Early recognition and source control
Infected patients are the main source of pathogens in health-care settings, and reducing or preventing the dissemination of the infectious agent from the source is critical. These methods of reduction and prevention include promotion of respiratory hygiene (Annex B, Section B.1.3), early recognition and investigation, prompt implementation of IPC precautions, reporting and surveillance, and treatment to make patients non-infectious.
1.4.2. Administrative controls
The health-care facility management team needs to ensure that the necessary resources are available for implementation of IPC measures. These resources include the establishment of sustainable IPC infrastructures and activities; clear policies on early recognition of ARIs of potential concern; access to prompt laboratory testing for identification of the etiologic agent; implementation of appropriate IPC measures (e.g. Standard Precautions for all patients), and appropriate clinical triage and placement of patients; provision of regular supplies; and organization of services. The management team should also undertake staff planning to promote an adequate patient-to-staff ratio, provide staff training, and establish appropriate programmes for staff vaccination and prophylaxis.
1.4.3. Environmental and engineering controls
Environmental and engineering controls aim to reduce the concentration of infectious respiratory aerosols (e.g. droplet nuclei) in the air and to reduce the contamination of surfaces and inanimate objects. Examples of primary engineering controls for infectious respiratory aerosols include adequate environmental ventilation and spatial separation, with a distance of at least 1 m between patients. Adequate environmental ventilation is especially important to reduce the transmission of pathogens that are transmitted through the airborne route (e.g. pulmonary TB, measles and chickenpox). For infectious agents that spread by contact, important environmental control methods include cleaning and disinfection of contaminated surfaces and inanimate objects.
1.4.4. Personal protective equipment
These strategies all serve to reduce, but do not eliminate, the possibility of exposure to respiratory pathogens. The appropriate use of PPE serves to further reduce the risks of transmission of respiratory pathogens to health-care workers and other people interacting with the patients in the health-care facility. The use of PPE should be defined by policies and procedures addressing isolation precautions. Their effectiveness depends on adequate and regular supplies, adequate staff training, proper hand hygiene and, in particular, appropriate human behaviour.
All these controls are connected and should be harmonized to promote an institutional culture of safety.
1.5. Guideline development process
These guidelines were developed according to the WHO handbook for guideline development, 2012 (18). WHO commissioned systematic reviews and critical reviews of the literature as applicable. Every attempt was made to develop recommendations that focused on priority or controversial areas, using systematic reviews and evidence summaries according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach (18, 46-50) (Annex K). The GRADE approach provides a structured and transparent assessment of the quality of evidence and its application to the guidelines process. A hierarchical approach was used to review the evidence when formulating the recommendations in these guidelines, with the highest ranking given to systematic reviews of human studies. Quality of evidence was ranked from randomized trials (deemed to be of highest quality), followed by prospective cohort studies, retrospective cohort studies, and finally controlled before-and-after studies (lowest quality). Similarly, priority of studies was ranked from in vivo animal studies relevant to the topic (deemed to be of highest priority) to in vitro laboratory studies relevant to the topic and theoretical considerations (lowest priority). The scientific evidence was also assessed for inconsistency, indirectness, imprecision, reporting bias, and other potential sources of bias. The summaries of each systematic review are provided in the Annex L, and the evidence profiles are available in published systematic reviews and referenced in the decision tables (Annex K) and in the Annex L.
Quality of evidence was considered of major importance in developing the guidelines. In addition, we considered the balance of the benefits or desired effects versus the disadvantages or undesired effects; values and preferences from a global perspective, including those of front-line health-care workers; cost and resource implications; and the feasibility of adopting a recommendation (18, 46-50). The recommendations were discussed internally with a Working Group within WHO, and then submitted to members of the Global Infection Prevention and Control Network (GIPCN) for review and feedback. Following the technical consultation meeting with the GIPCN, additional changes were made. The draft of these guidelines was also submitted for broad internal and external review.
