Public Health and Infectious Disease
Public Health and Infectious Disease
Public Health and Infectious Disease
An effective response to an infectious disease outbreak, epidemic, or pandemic requires a coordinated approach from all parts of the public health system. Public health units play an important role in disease control and response including planning for emergencies, surveillance, education, communication, case identification, case management, infection control, contact tracing, monitoring contacts in quarantine, border surveillance, epidemiological studies, and immunization.
The disease surveillance system must ensure that the first cases of the outbreak are quickly identified. Next, controls trategies must be implemented to slow down the transmission of the pathogen while a vaccine or effective treatments are being developed. Surveillance would also detect the final case, indicating an end to the outbreak.
The Infectious Disease Surveillance System in the United States
Reporting of Communicable Diseases When a known “notifiable” disease or an unknown communicable disease is suspected to be a public health threat, clinicians should immediately notify the local health authority. Reporting requirements vary greatly from one region to another because of different conditions and different disease frequencies.
Communicable disease reporting is necessary to provide accurate and timely information for the initiation of investigation and control measures. It also encourages uniformity in morbidity and mortality reporting so that data among different health jurisdictions within a country and among nations will be consistent and comparable.
A reporting system functions at four levels:
- Collection of basic data on incidence, geographic dispersion, and patient outcomes in the local community where the disease occurs.
- Assembly of data at district, state, or provincial levels.
- Aggregation and analysis of the information at the national level.
- For certain designated diseases, the national public health agency reports data and analysis to the World Health Organization (WHO).
Reporting of Cases Each local health authority determines what diseases should be routinely reported. Physicians are required to report all notifiable illnesses that come to their attention. In addition, the statutes or regulations of many localities require reporting by hospital infectious disease officers, householders, or other persons having knowledge of a case of a reportable disease. These may be individual case reports or reports of groups of cases (collective reports).
Reporting of Epidemics For reporting purposes, diseases are usually classified into the following five classes, according to the advantages that can be derived from reporting. This classification provides a basis for inclusion in a local list of regularly reportable diseases. Case finding can be passive, i.e., the physician initiates the report as required, or active, when the public health officer regularly contacts clinicians, clinics, or hospitals to request the desired information.
Class 1: Case Report Universally Required by International Health Regulations or as a Disease under Surveillance by the WHO. This class can be divided into the following types:
- 1: Those diseases subject to the International Health Regulations (1969), 4th Annotated Edition 2005, WHO, Geneva: e.g., the internationally quarantinable diseases such as plague, cholera, and yellow fever.
- 1A: Diseases under Surveillance by WHO, established by the 22nd World Health Assembly: e.g., louse-borne typhus fever and relapsing fever, paralytic poliomyelitis, malaria, and influenza.
The required case report is made to the health authorities by telephone, FAX, telegraph, or other rapid means; in an epidemic situation, collected reports of subsequent cases in a local area may be requested by the next superior jurisdiction on a daily or weekly basis. The local health authority forwards the initial report to the next superior jurisdiction by the most expeditious means.
Class 2: Case report regularly required wherever the disease occurs. Two subclasses are recognized, based on the relative urgency for investigation of contacts and source of infection, or for starting control measures. Examples include typhoid fever and diphtheria, brucellosis, and leprosy.
Class 3: Selectively reportable in recognized endemic areas in many states and countries; diseases of this class are not reportable. Reporting may be prescribed in particular regions, states, or countries if they recur with undue frequency or severity. Three subclasses are recognized, based on urgency of the investigation or control measures. Examples are scrub typhus, arenaviral hemorrhagic fever, bartonellosis, coccidioidomycosis, schistosomiasis, and fasciolopsiasis.
Class 4: Obligatory report of epidemics—no case report required. Pertinent data include number of cases, time frame, approximate population involved, and apparent mode of transmission; e.g., staphylococcal foodborne intoxication, adenoviral keratoconjunctivitis, unidentified syndrome.
Class 5: Official Report Not Ordinarily Justifiable. Diseases of this class are of two general kinds: those typically sporadic and uncommon, often not directly transmissible from person to person (chromoblastomycosis), or those with an epidemiology that offers no special practical measures for control (common cold).
Diseases are often made reportable, but the information gathered is not put to practical use with no feedback to those who provided the data. This can lead to deterioration in the general level of reporting, even for diseases of critical importance. Better case reporting results when official reporting is restricted to those diseases for which control services are provided or potential control procedures are under evaluation, or epidemiologic information is needed for a definite purpose.
Public Health Response to SARS
In 2003 the world experienced the sudden onset of an epidemic of the virulent disease severe acute respiratory syndrome or SARS. The response to this outbreak was the first opportunity for new global public health surveillance and control agencies to act in anticipation of a potential avian influenza outbreak. The infectious agent was a highly pathogenic virus (in this case a coronavirus). Like the anticipated pattern for avian flu, the outbreaks spread from Asia to the rest of the world. Thus, the SARS epidemic was a trial run of emerging international public heath protocols to identify and respond to infectious disease threats.
The largest outbreak of SARS began in March 2003 in Beijing, China. This outbreak was resolved within six weeks of its peak in late April. Chinese public health agencies recorded case data from SARS cases observed in Beijing and their close contacts between March 5, 2003, and May 29, 2003 onto standardized surveillance forms, which were subsequently reviewed by epidemiologists. The epidemiological investigation focused on 1) the response of public health agencies to the SARS outbreak in terms of the timeline for implementing major control measures; 2) the number of reported cases and quarantined close contacts; 3) the calculated attack rates, with changes in infection control measures, management, and triage of suspected cases; and 4) the time lag between illness onset and hospitalization with information dissemination.
The investigation found that health care worker training in use of personal protective equipment and the isolation of patients with SARS, along with the establishment of fever clinics and designated hospital SARS wards, predated the steepest decline in cases. During the outbreak 30,178 exposed persons were quarantined in China. Attack rates among quarantined individuals were calculated by type of relationship to known victims and the age of the contact. Among 2,195 quarantined close contacts in five districts, the attack rate was 6.3%, with a range of 15% among spouses to less than 0.5% among work and school contacts. The attack rate among quarantined household members was found to increase with age from 5% in children younger than 10 years to 27% in adults aged 60 to 69 years.
Among nearly 14 million people screened for fever at airports, train stations, and roadside checkpoints, only 12 were found to have probable SARS. After initial reticence, the national and municipal governments adopted a policy of full disclosure, holding 13 press conferences about the SARS outbreak. Following the installation of strict screening and control procedures, the time interval between illness onset and hospitalization decreased from a median of five to six days on or before April 20, 2003, the day the outbreak was announced to the public, to two days after April 20. The rapid resolution of the SARS outbreak was due to multiple factors, including improvements in patient isolation and triage in both hospitals and communities of patients with suspected SARS and the propagation of information to health care workers and the public.
On the other side of the globe, the largest SARS outbreak in North America occurred in Toronto, Canada. Again, epidemiologists analyzed the patterns of transmission and the public health effects of control measures, and the findings and disease patterns closely paralleled those in China. Toronto Public Health examined 2,132 potential SARS cases, ascertained that 23,103 contacts of SARS patients required quarantine, and logged 316,615 calls on a hotline dedicated to SARS. According to the investigators, 225 Toronto residents met the case definition of SARS. Only three travel-related cases were not linked to the index patient, who came to Toronto from Hong Kong.
WORDS TO KNOW
INFECTION CONTROL: Infection control refers to policies and procedures used to minimize the risk of spreading infections, especially in hospitals and health care facilities.
MORBIDITY: The term “morbidity” comes from the Latin word “morbus,” which means sick. In medicine it refers not just to the state of being ill, but also to the severity of the illness. A serious disease is said to have a high morbidity.
MORTALITY: Mortality is the condition of being susceptible to death. The term “mortality” comes from the Latinword mors, whichmeans“death.” Mortality can also refer to the rate of deaths caused by an illness or injury, i.e., “Rabies has a high mortality.”
NOTIFIABLE DISEASE: A disease that the law requires must be reported to health officials when diagnosed; also called a reportable disease.
QUARANTINE: Quarantine is the practice of separating people who have been exposed to an infectious agent but have not yet developed symptoms from the general population. This can be done voluntarily or involuntarily by the authority of states and the federal Centers for Disease Control and Prevention.
PANDEMIC: Pandemic, which means all the people, describes an epidemic that occurs in more than one country or population simultaneously.
SURVEILLANCE: The systematic analysis, collection, evaluation, interpretation, and dissemination of data. In public health, it assists in the identification of health threats and the planning, implementation, and evaluation of responses to those threats.
A resurgence of the outbreak occurred due to unrecognized SARS among hospitalized patients. This was eventually controlled using active surveillance of hospitalized patients. The control measures of Toronto Public Health brought about a reduction in the number of persons exposed to SARS in non-hospital and nonhousehold settings from 20 before the control measures were implemented to zero after implementation. The number of patients exposed while in a hospital ward rose from 25 before the measures were taken to 68 afterwards, while the number exposed during a stay in the intensive care unit dropped from 13 to zero. The spread of the outbreak in the community (outside of hospital settings) was significantly reduced after instituting the control measures.
Toronto SARS transmission was mostly limited to hospitals and households where patients had contacts. Epidemiologists determined that for every case of SARS, public health authorities could expect to quarantine up to 100 patient contacts and investigate eight potential cases. Active in-hospital surveillance for SARS-like illnesses and heightened infection-control measures were essential in bringing the outbreak under control.
Although the public health response to SARS was successful within a short time-frame, it is far from clear that a similar response to an avian flu outbreak would be as successful, mainly because influenza mortality and infectivity could be much greater, while current treatments could be considerably less effective. For this reason, the production of an effective avian flu vaccine is seen as essential for controlling an avian flu outbreak.
Control of Infectious Disease Outbreaks
Once an outbreak of infectious disease has been detected, public health agencies must consider a range of disease control measures from the control of patient contacts and the immediate environment of the outbreak to mass vaccination programs or mass prophylaxis using anti-infective medication. Following are some examples of recent research and a discussion of the use of certain control measures in the context of public concern over the possibility of an avian flu pandemic.
Risks of Mass Vaccination and Prophylaxis as Disease Control Measures As public health experts consider the implications of serious infectious disease outbreaks, they must balance the potential benefits of control measures such as mass immunization. One consideration that leads to caution in implementing such measures is the occurrence of relatively rare but predictable adverse reactions or events due to vaccination or medication (medication-related adverse events or MRAEs). For example, it is generally considered unacceptable to incur predictable mortality by using vaccines that have a rate of adverse reactions, however low, unless there is an actual outbreak of a dangerous disease. Computer models for particular infectious diseases can calculate outbreak-specific predicted daily MRAE rates from model user inputs by applying a probability distribution to the reported timing of MRAEs. One such exercise modeled a hypothetical 2to 10-day prophylaxis operation for one million people using recent data from both smallpox vaccination and anthrax antibiotic prophylaxis campaigns. It was found that the duration of a mass prophylaxis campaign is important in determining the ensuing amount of emergency services utilization due to actual or suspected adverse reactions. In a population of that size, a 2-day smallpox vaccination scenario would produce an estimated 32,000 medical encounters and 1,960 hospitalizations, peaking at 5,246 health care encounters six days after the start of the campaign. By contrast, a 10-day campaign would lead to a much lower peak surge, with a maximum of 3,106 encounters on the worst day, 10 days after campaign initiation.
Thus the duration of a mass prophylaxis campaign could have a significant impact on the timing and peak number of serious MRAEs, with very brief campaigns overwhelming existing emergency department (ED) capacity to treat real or suspected adverse reactions. Although these results could be refined by further study of adverse reaction rates, the results of modeling underline the necessity for coordinating public health and emergency medicine planning for infectious disease outbreaks in order to avoid preventable surges in ED use.
Travel Restrictions as a Disease Control Measure Travel restrictions have often been suggested as an efficient way to reduce the spread of a communicable disease that threatens public health. Swedish researchers conducted a computer simulation of the effect of different levels of travel restrictions on the rapidity and geographical spread of an outbreak of a disease similar to SARS. They tested scenarios of travel restrictions in which travel over distances greater than 30 mi (50 km) and 12 mi (20 km) would be banned, taking into account different compliance levels. They found that a ban on journeys over 30 mi (50 km) would drastically reduce the speed and geographical spread of outbreaks, even when compliance is less than 100%. Their study supported the use of travel restrictions as an effective way to mitigate the effect of a future disease outbreak, at least when the infectivity of a disease is moderate as in the case of SARS. It is not known how effective they will be for airborne and animal borne infections with greater transmissibility such as a potential mutant H5N1 virus, discussed in more detail later.
Medication Stockpiles as a Potential Control Measure As noted earlier, much of the discussion and research regarding infectious disease control measures has happened in the context of concern about a potential new worldwide influenza pandemic, such as happens about three times each century. The worst of these pandemics on record was the 1918 pandemic, which killed at least 20 million people. H5N1 flu has become endemic in Asian birds, and at least 74 human cases, including 49 deaths and probable human-to-human transmission, have occurred since the beginning of 2004. International health officials lack the resources to monitor avian flu in a population of hundreds of millions in the parts of Asia likely to become the epicenter of such a new pandemic, including some countries with rudimentary or no public health systems.
If such a pandemic reached the United States at the present time, it would be possible to manufacture only enough vaccine for perhaps a quarter of the population. The currently planned domestic stockpile of oseltamavir would leave over 99% of the country unprotected. In contrast, Great Britain's planned stockpile will be 25 times greater on a per-capita basis, and some authorities suggest that even that level is insufficient. To change the course of such a pandemic, vaccines and antiviral drugs will be needed in much greater quantities than current plans allow.
Most researchers agree that pandemic influenza will recur. The world's surveillance systems and countermeasures are likely inadequate, and current control measures may not significantly slow a pandemic once it has begun.
In June 2006 in the Commonwealth of Massachusetts, a panel of national, state, and local experts met to assess the threat of an avian influenza pandemic. In particular, they discussed the readiness of state and local officials response to such a pandemic. The conference leaders suggested that political entities, the public health system, and the medical community need a “seamless network of protection” against this potentially lethal threat. Three major challenges to pandemic planning and preparedness were noted: 1) the scale of the challenge; 2) connectivity of communication; and 3) the danger of complacency.
The current threat posed by avian influenza was described at the conference as requiring monitoring for mutations in the virus and its ability to transmit efficiently among people, particularly since there is no immunity among human populations against H5N1. Also, the ease and frequency of international travel and transportation of goods means that an evolving threat anywhere in the world is a threat everywhere.
Attendees noted that the response to the SARS epidemic conveyed some valuable public health lessons. Among these was that travel advisories seemed to help to contain the SARS pandemic. Interventions such as social distancing (e.g., cancellation of large gatherings, quarantining persons infected with influenza, and the use of cough etiquette and masks) could be helpful in mitigating the effects of an influenza pandemic. Two scenarios of an avian flu epidemic in the United States were discussed. One was based upon the 1957–1958 (swine flu) pandemic, and one upon the more severe 1918 (Spanish flu) pandemic. Both scenarios assume that 30 percent of the current U.S. population will become ill; up to half of those who are ill will require outpatient medical care.
The major difference between the scenarios would be the severity of the illness. If the pandemic is moderately severe, as it was in 1957, then approximately 209,000 people in the United States could die. However, if the pandemic causes severe disease, estimates show that almost 10 million people would require hospitalization, with 1.5 million requiring ICU care. Data from the 1918 pandemic indicate that close to 2 million deaths could occur in the United States alone, and millions more worldwide.
The federal government has made it clear that, in the event of a pandemic, it will not be able to respond to every community. Rather, state and local jurisdictions must take responsibility for preparedness planning and response efforts. Basic public health tools, including good communication about risk, individual/family/community preparedness, identification and quarantine of confirmed cases, and social distancing could be most useful during the initial stages of a pandemic. Schools and businesses could choose to temporarily close and use technology to reduce direct contact between people.
Effective communication during a pandemic is essential. Since it is possible that the supply chain of services, goods, and food will be disrupted during a severe pandemic, it is recommended that individuals and families store at least a two-week supply of water and food, nonprescription drugs, and other health supplies including pain relievers, stomach remedies, cough and cold medicines, fluids with electrolytes, and vitamins. The CDC addresses these concerns and provides a number of preparedness checklists and other tools on their website, <www.pandemicflu.gov> .
In Massachusetts, the state's pandemic preparedness plan is “intended to ensure that essential services are maintained, there is minimal discomfort and loss of life, the most vulnerable are cared for and that individuals, families and first responders are protected.” The plan addresses hospital and health care facility surge capacity and staffing issues, surveillance and identification of influenza, the health and safety of vulnerable populations, timely and effective communication, and continuity of government and essential services during a crisis.
Massachusetts executive branch agencies that oversee critical services have submitted mandatory “continuity of government” (COG) plans to ensure that critical operations will continue during a pandemic. Businesses, schools, colleges and universities, providers, and municipal governments should all be preparing “continuity of operations plans” (COOPs) in order to ensure contingencies be made in the event of a pandemic. Educational outreach programs have begun and, to date, a number of impact estimates have been done in the state detailing the possible outcomes of an influenza pandemic. Legislation is pending that would indemnify emergency volunteer health workers and make them eligible for workers’ compensation, which is important to recruiting needed staff. The administration will disseminate directives on how quarantine should be declared, what travel restrictions might result in the event of a pandemic, and where influenza specialty care clinics (ISCUs) are located. Simulation exercises have been conducted and public information campaigns have begun.
Five regional pandemic planning conferences have been held across Massachusetts that brought together representatives from public health and safety, business, healthcare, local government, primary and secondary schools, higher education, and the faith and human services communities. Among recommendations were improved hospital surge capacity, recruitment of volunteer healthcare staff, and increased state laboratory surveillance capabilities and stockpiles of antivirals.
Within Massachusetts there are a number of agencies and institutions that will be involved in the initial stages of a pandemic. Communities, businesses, schools, and individuals must be kept informed as a pandemic unfolds. A challenge at the local level is for public health officials to communicate effectively with other emergency responders that do not necessarily speak the same public health language.
Some critics assert that local public health officials are also being asked to conduct training, generate plans, and purchase supplies in preparation for a potential flu pandemic, but may lack the necessary resources and infrastructure to carry out their plans. Additionally, some community officials feel that they are not being included in federal and statewide planning.
To address these issues, the state has included each of the 351 local boards of health into one of 15 Emergency Preparedness Coalitions of contiguous municipalities in an effort to facilitate joint planning and resource distribution. The Coalition holds monthly planning meetings, allocates resources to local public health agencies, facilitates collaboration with area hospitals, evaluates training needs, and holds drills and regional flu clinics. These regional clinics were successful during the past influenza season and exemplified that collaboration within regions is possible.
Level of preparedness in Massachusetts
Many towns have created emergency plans, identified emergency dispensing sites, are running pandemic influenza drills, have a comprehensive response system in place, and are improving communication with other first responders. There is still insufficient long-term staffing, insufficient money to increase capacity, and the emergency personnel pool is inadequate. A clear definition of the role of local public health departments and joint planning strategies between towns are required, since there is tremendous variation across communities in terms of needs and resources.
As increased migration and trade has heightened the threat of pandemic disease, cooperation among national governments and public health organizations worldwide has become essential. Since pandemic infectious diseases spread across national borders, disease prevention measures in one nation affect surrounding nations as well. The following article from the New York Times asserts that some pandemic influenza prevention measures disproportionately affect the poorest residents in regions where the disease is likely to emerge.
Ruth R. Faden is executive director and Patrick S. Duggan is research coordinator, both at the Berman Institute of Bioethics at Johns Hopkins. Ruth Karron is the director of the Center for Immunization Research at the Johns Hopkins Bloomberg School of Public Health.
Who Pays to Stop a Pandemic?
BIRD flu has not yet turned into a pandemic, but it is already killing the meager hopes of some of the world's poorest people for a marginally better life.
When poultry become infected with the deadly strain of avian influenza (H5N1), it is essential that all birds nearby be culled to prevent further spread. We all stand to benefit from this important pandemic prevention strategy, recommended by the World Health Organization and the United Nations Food and Agriculture Organization. Unfortunately, however, the world's poor are unfairly shouldering the burden of the intervention.
Last month officials in Jakarta, Indonesia, announced a ban on household farming of poultry there. The domestic bird population of Jakarta is estimated at 1.3 million. Thousands of families were given until Feb. 1 to consume, sell or kill their birds. Now inspectors are going door to door to destroy any remaining birds.
The Indonesian government pledged to pay about $1.50 for each bird infected with the H5N1 virus, a sum that may approximate the bird's fair market value. But most birds that have been killed under this policy are healthy, so their owners, most reports suggest, will receive nothing.
Moreover, it is not clear how Jakarta's poor will replace the income they once received from chickens and other birds. When officials impose widespread culling, industrial-scale poultry producers—like the company that owns the large British turkey farm where bird flu was found this month—usually have the resources to absorb the losses. But when the birds of small-scale poultry farmers are culled, entrepreneurs who were just beginning to move up the development ladder can be plunged right back into poverty. The most dependent and vulnerable members of the community become even more dependent and vulnerable. “Backyard birds” are the only source of income for many women and children.
Families whose birds are found to be infected with the virus may suffer even more. People in Cambodia, China and India whose poultry have been blamed for avian influenza outbreaks have often been subject to extreme stigma and isolation, and there have even been reports of suicides by desperate farmers.
It is inevitable that the world's poor will suffer most from a pandemic. A recent article in The Lancet predicted that if the next pandemic were to mimic the huge 1918 flu outbreak, 96 percent of an estimated 62 million deaths would occur in developing countries. But specific steps can and should be taken now to prevent or mitigate the injustices that are already occurring.
We are part of a group of 24 government officials, public health experts and scientists from 11 countries who recently met in Bellagio, Italy, with the support of the Rockefeller Foundation to call attention to how pandemic planning affects the world's disadvantaged. We created a checklist for avian influenza control that explicitly calls on the authorities to compensate people who suffer losses from bird-culling programs, regardless of whether the destroyed birds are infected with the avian influenza virus.
Such a program in Jakarta alone would be expensive. Just to compensate families for their culled birds would require nearly $2 million, not including the cost of administering the program. Indonesia's domestic bird population countrywide is estimated at 300 million, so if the culling program were to be expanded beyond Jakarta, the total compensation cost could run as high as $450 million.
Indonesia's avian influenza budget for the coming year is reported to be less than $50 million. Clearly, without donor assistance, the government cannot afford to compensate families and farmers fairly. So the burden of pandemic prevention must also fall on the world's wealthy nations.
Last year, the United States, the European Union and other nations pledged more than $2billion to the global war chest for avian influenza response. Developing a program to compensate poor families in countries with limited resources is an enormous challenge. But it is time that the money pledged by the donor countries reach the people who are already the first victims of the next pandemic.
Ruth R. Faden, Patrick S. Duggan, and Ruth Karron
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Kenneth T. LaPensee