Introduction
Chain of infection
Primary vs. secondary control
Notification of potential outbreaks
Advantages of early detection
Issues with late detection
Diagnostic testing
References
Further reading
Infectious disease is the cause of a good deal of morbidity and mortality among individuals in the community and hospitals. While much of it is sporadic and isolated, most infections tend to spread, making an outbreak likely to occur. This can cause unnecessarily high rates of disease and debilitation and even death.
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Introduction
In typical cases, an infectious pathogen enters a susceptible host and begins to multiply. This leads to the incubation period before the results of the proliferation of the pathogen become manifest. This is followed by the onset of symptoms, a self-assessment by the patient, and a search for information as to the cause of the symptoms.
Eventually, if serious enough to warrant concern, the patient may visit a doctor, and diagnostic protocols are put in place, beginning with a medical assessment. This is followed by confirmation of the diagnosis and treatment or spontaneous resolution. The outcome may vary from complete recovery to death.
Chain of infection
The 'chain of infection' refers to the spread of the infectious agent in a community via several steps that are linked to one another. They include the pathogen itself, the reservoir of the pathogen, how it escapes from the reservoir, the mode of transmission, the means of entry into a susceptible host, and the host itself.
Infectious agents include bacteria, fungi, viruses, and parasites. Reservoirs include humans, animals, insects, plants, soil, or other substance that provides essential conditions where pathogens live and multiply under normal conditions. The pathogen may leave the reservoir by blood or other body fluids. For instance, a cough may transmit a respiratory virus such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from an infected individual to another person.
The mode of entry includes inhalation, skin contact leading to entry into a body orifice, or the ingestion of contaminated substances, to name the most important. The susceptible host allows the virus to enter and establish infection.
Primary vs. secondary control
Infectious disease control is an urgent matter in reducing disease incidence, decreasing its prevalence, or even eradicating it. The control of the infection is meant to break the chain of transmission of the pathogen.
When the control measures are meant to reduce the incidence of infectious disease or its risk factors, they come under the umbrella of primary prevention. Such measures include immunization, good nutrition, physical fitness, hygiene and sanitation, and a safe water supply.
The second type of control measure focuses on cutting short the infectious period and thus preventing or reducing transmission of the infectious agent. This is called secondary prevention and includes screening for infection to promote its early detection, with prompt treatment of those found to be infected, even if they are asymptomatic.
Notification of potential outbreaks
Easily transmissible diseases are caused by pathogens that have high infectivity and transmissibility. Early detection of the pathogen is thus essential to put containment measures in place early enough that large-scale containment is rendered unnecessary, especially when resources are scarce.
For this reason, a notification system is often implemented so that public health authorities are made aware of potential outbreaks in a timely manner. Notification will trigger an investigation of the potential outbreak that can help arrest its spread. While in most cases, minor outbreaks occur, having this type of system in place pays off richly when larger epidemics or pandemics happen
Advantages of early detection
Limiting outbreak size
Transmission of an infectious disease depends on a high number of contacts between the cases and other individuals, as well as a high rate of dispersion of the contacts in the population. It is important to diagnose the infection and the causative organism as early and accurately as possible so that the right intervention (including measures such as isolation and quarantine) can be put in place to confine the infection and prevent its spread.
Constant surveillance is necessary to identify potential outbreaks and track the spread of the pathogen. Without this, transmission continues, causing worldwide spread as with the repeated influenza pandemics or ongoing serious infections as with the human immunodeficiency virus (HIV).
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A core strategy to minimize the risk posed by widespread infectious diseases is the development of a surveillance system to quickly identify potential outbreaks as early as possible accurately, such that an effective intervention plan can be implemented before the substantial costs associated with the spread of diseases have been incurred."
The earlier the infection is detected, the smaller the eventual size of the outbreak. Contact tracing being unsustainably resource-greedy, other methods of early detection are therefore being sought. This is particularly the case with infectious diseases with a high proportion of asymptomatic disease.
Issues with late detection
In some cases, as with rubella, the spread of the pathogen via asymptomatic or mildly symptomatic undiagnosed patients may be extremely risky, as when the secondary case happens to be pregnant. Rubella is highly teratogenic, though the viral infection in most children and adults is very mild. The fetus may die in utero or be born with severe and multiple congenital anomalies, causing a high financial, social and emotional burden to the family and society.
Again, suppose an infection is spreading rapidly. In that case, hospitals, clinics, outpatient facilities, healthcare workers, and medical equipment or drugs must all be prepared and stockpiled to meet a potential state of emergency. This requires a timely diagnosis of the infection and its trajectory, both on the level of severity and also of the scale of the outbreak.
The failure to diagnose an infection accurately and early can also lead to antibiotic overuse or misuse, a major factor in the emergence of antimicrobial resistance. Early diagnosis could have avoided this by clarifying that the infection is or is not susceptible to the proposed treatment.
Many infectious diseases cause long-term complications, including cancers or deadly chronic disease. For instance, high-risk strains of the human papillomavirus (HPV) cause cervical cancer, while Helicobacter pylori can cause not only peptic ulcers with their attendant potentially deadly sequelae but stomach cancer. Both hepatitis B and hepatitis C viruses can cause chronic hepatitis and liver cancer.
As infectious diseases progress, many severe complications may threaten the patient's life or long-term health. Wound infection must be diagnosed early, for instance, to prevent life-threatening sepsis and multi-organ dysfunction.
Thus, apart from the need to prevent the further spread of an infectious condition, early diagnosis is critically important to safeguard the individual's health as well by increasing the likelihood of appropriate treatment that will clear the pathogen from the host tissues.
Diagnostic testing
At present, there is a wealth of technologies to detect infections easier and faster than ever before. Not only the type of pathogen but even the specific genetic pattern can be identified, helping to track the strain back to the source and thus identify the cause of the infectious outbreak.
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New diagnostic tests are being developed all the time to diagnose infections early enough to meet all these needs. Multiplexed tests such as BioFire's FilmArray can rule out multiple organisms simultaneously.
Tests such as matrix-assisted laser desorption time of flight (MALDI-TOF) mass spectrometry can reduce the time required to identify a cultured organism, from weeks, days, or hours to mere minutes, from blood samples or urine. Nucleic acid testing is also here to stay, especially multiplexed platforms that search for more than one pathogen simultaneously.
Ribosomal ribonucleic acid (rRNA) is being used to identify bacteria in clinical tests, while the intergenic transcribed spacer (ITS) and 28S rRNA regions in fungi allow their rapid detection along with the more cumbersome techniques based on morphology. Next-generation sequencing (NGS) allows for individual samples to be profiled, as well as communities of microbes. The advent of polymerase chain reaction (PCR)-electrospray ionization (ESI) mass spectrometry is also a promising development for microbial identification.
Other tests include protein antigen identification, both lateral flow assays, and fluorescent immunoassays, often used for screening. Immunohistochemistry is used on fixed specimens.
Besides such tests, either centralized or used at the point of care (POC), Big Data may detect or warn of outbreaks early enough to abort them or limit their final size. Such systems are being set up and may include mobile phone data, internet searches for infection-related terms, and electronic dashboards to encourage timely and complete recording of infectious disease outbreaks.
References
Further Reading
Global study reports significant decline in diarrheal disease mortality