Strep Throat (Streptococcal Pharyngitis)

Strep throat or streptococcal pharyngitis is caused by group A Streptococcus bacteria and is the most common bacterial infection of the throat. Although this infection can occur at any age, it is most common in children between the ages of 5 and 15 years. Strep throat is transmitted by person-to-person contact via nasal secretions or saliva (sneezing and/or coughing) by an infected individual or a carrier. On occasion, contaminated food, especially milk and milk products, may be the cause of the infection.

The infection occurs with higher frequency in the late fall, winter, and early spring. Most sore throats are caused by viruses, not by bacteria, and therefore the Centers for Disease Control and Prevention (CDC, Atlanta, GA) recommends that antibiotics not be used unless the test for streptococcal infection proves to be positive, because bacterial resistance to certain antibiotics has been reported. However, if results are positive for Streptococcus, patients should receive antibiotics to minimize transmission and to reduce the risk of further complications, such as rheumatic fever.

Scarlet Fever

Scarlet fever is an upper respiratory disease also caused by an infection with a group A β-hemolytic streptococcus (Streptococcus pyogenes) (Figure 11.2) and once was a serious childhood disease but now is generally treatable. The incubation period is 1 to 2 days and typically begins with a fever and sore throat, but might also exhibit chills, vomiting, abdominal pain, and malaise. The exotoxin produced by the bacteria is responsible for the “strawberry” tongue (Figure 11.3) as well as the characteristic fine rash on the chest, neck, groin, and thighs. The treatment of scarlet fever is the same antibiotic treatment as for strep throat, and complications with appropriate treatment are rare.

Streptococcus pneumoniae

Streptococcus pneumoniae is a gram-positive, encapsulated α-hemolytic diplococcus (Figure 11.4), also known as pneumococcus, and is a common cause of mild respiratory illness, but also a major source of pneumonia. Other than pneumonia the organism is also capable of causing pharyngitis, sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, cellulitis, and brain abscess. S. pneumoniae is a common inhabitant of the nasopharynx of healthy people, but can be the cause of disease when the organism reaches other areas such as the eustachian tubes, nasal sinuses, and lungs. Furthermore the organism can be found in larger numbers in environments where people spend a lot of time in close proximity and it can be transmitted by person-to-person contact or by inhalation. If the organism is inhaled and not removed by the ciliary escalator (such as in smokers, in whom the cilia have been damaged or degenerated), or the mucous membranes are damaged by a viral infection, the bacteria can attach or even penetrate the mucosa. Once the organism succeeds in getting to a site where it normally is not found it will stimulate the immune system of the host, resulting in the attraction of leukocytes (see Chapter 20, The Immune System). The capsule of S. pneumoniae is resistant to phagocytosis and if immunity is not present the alveolar macrophages are incapable of destroying pneumococci. In this case the bacterium spreads into the bloodstream, where it most likely causes bacteremia. The organism then can get to other areas of the body, causing the conditions mentioned earlier. The virulence of S. pneumoniae is a direct result of its capsule and the encapsulated (smooth) strains are the ones causing disease, whereas the nonencapsulated (rough) strains are avirulent.

The onset of bacterial pneumonia can vary from gradual to sudden. In severe cases patients may have fever, shaking chills, shortness of breath, cough with rust-colored or greenish mucus, and pleuritic chest pain. Fever and sputum production may be absent in elderly persons with pneumococcal pneumonia. Pneumonia can sometimes appear in a mild form, often referred to as “walking pneumonia,” in which symptoms are slight or absent. The risk for bacterial pneumonia is highest for young children, the elderly, people with chronic medical conditions (e.g., heart disease, lung disease, and diabetes), and persons who have a suppressed immune system. Because bacterial pneumonia can easily be passed from one member of the community to another, it can manifest itself in a condition referred to as “community-acquired pneumonia.” This form of the disease occurs worldwide and is a major cause of death among all age groups.

Vaccination is available for the prevention of pneumococcal pneumonia. Two vaccines are currently available: the pneumococcal conjugate vaccine, which is part of the routine infant immunization schedule, and the pneumococcal polysaccharide vaccine used for adult immunization. Vaccination with the pneumococcal polysaccharide vaccine is recommended for all adults age 65 years and older and for persons 2 to 64 years of age with certain chronic illnesses or immunocompromising conditions. Without vaccination the treatment of choice used to be penicillin; however, because of overuse of antibiotics nearly all strains of S. pneumoniae previously susceptible to penicillin show resistance to penicillin as well as to other antibiotics.

Drug-resistant Streptococcus pneumoniae Disease

Drug-resistant Streptococcus pneumoniae disease (DRSP) manifests itself as pneumonia, bacteremia, otitis media, meningitis, peritonitis, and sinusitis. These conditions can be caused by an organism that is resistant to one or more commonly used antibiotics. Overuse of antimicrobial agents is a contributing factor to the emerging resistance and spread of resistant strains. Transmission occurs by person-to-person contact and the risk groups are mostly the elderly, children 2 years of age or older, persons who attend or work at child care centers, immunocompromised patients (e.g., those with AIDS), and also persons who recently used antimicrobial agents. Outbreaks of DRSP have been reported in nursing homes, child care centers, and in institutions for HIV-infected people. A pneumococcal conjugate vaccine is available and its use is preventing many infections due to drug-resistant pneumococci. Future increased use of the vaccine, systematic surveillance, and routine testing for the drug-resistant strains might slow down the emerging drug resistance of this bacterium.

Chlamydial Pneumonia

Chlamydia pneumoniae, now called Chlamydophila pneumoniae, is one of the major causes of pneumonia or bronchitis and is characterized by a gradual onset of cough, with little or no fever. The spectrum of the illness can range from asymptomatic infections to severe disease. Transmissions occur through respiratory secretions of an infected individual and all ages are at risk; however, according to the CDC, it is most common in school-age children. Because the disease is easily passed from one member of the community to another it can give rise to “community-acquired pneumonia.” The infection can be treated with antibiotics and generally the drug of choice is erythromycin.

Pertussis (Whooping Cough)

Pertussis, also known as whooping cough, is a highly contagious disease caused by Bordetella pertussis, an extremely small, aerobic, gram-negative coccobacillus (Figure 11.6). It is a serious disease that can cause permanent disability and even death. Pertussis is easily spread from person to person by airborne droplets discharged from the mucous membranes of infected people. Initial symptoms occur about a week after exposure and resemble those of the common cold. The severe coughing spells start approximately 10 to 12 days later and these spells may lead to vomiting. The coughing often ends with a “whoop” noise caused when the patient is trying to take a breath. Despite the availability of, and high coverage with vaccines, pertussis is one of the leading causes of vaccine-preventable deaths worldwide. Ninety percent of all cases occur in the underdeveloped countries and most deaths involve infants who are either not vaccinated or incompletely vaccinated. Treatment with effective antibiotics, if started early, shortens the infectious period but usually does not alter the outcome of the disease.

Tuberculosis

Tuberculosis (TB) is a deadly infectious disease caused by Mycobacterium tuberculosis (Figure 11.7). TB is transmitted through the air when an infected person coughs, sneezes, or even talks. Moreover, TB is no longer a disease of the past; it is still a leading killer of young adults worldwide. TB is a chronic condition that usually infects the lungs, but other parts of the body might be involved as well. Most people infected with the organism do not show symptoms, but have latent tuberculosis. According to the World Health Organization (WHO, Geneva, Switzerland) estimate, annually 8 million people worldwide will develop active TB with nearly 2 million deaths. The risk for development of the disease is higher in the first year after infection, but the disease still can occur much later.

After the first effective antibiotic treatments were introduced (1940s and 1950s), the incidence of tuberculosis in the United States declined. The decline in new cases ended in 1985 and the incidence of TB started to rise again. According to the National Institute of Allergy and Infectious Diseases (NIAID, Bethesda, MD), several factors are responsible for this resurgence, such as the following:

Initial symptoms of active TB include weight loss (hence in the past, the disease was referred to as consumption), fever, night sweats, and loss of appetite. In the case of vague symptoms the infection might go unnoticed and can go into remission or become more chronic and debilitating. These symptoms include cough with chest pain and bloody sputum. Treatment is possible with appropriate antibiotics, which are generally effective, and most people can be cured. Successful treatment can last up to 12 months or longer, using different types of antibiotics. The success of the treatment also depends on the strain of the organism with which the patient is infected. Antibiotic-resistant strains are more difficult to treat, require different drugs, and an increased time of treatment might be necessary. If a person is infected with a strain that is resistant to two or more drugs the condition is called multidrug-resistant TB (MDR-TB), which is much more difficult to cure.

Tuberculosis can largely be prevented. In the United States health care providers attempt to identify people infected with M. tuberculosis as early as possible to prevent the development of active TB and the spread of the disease. Infected persons will receive isoniazid (INH) every day for 6 to 12 months to prevent active TB. Hospitals isolate people with active TB in controlled environments until spreading is no longer a threat.

TB vaccines are available and the WHO suggests that they be used in countries of the world where the disease is endemic. The vaccine is produced from a live weakened bacterium related to M. tuberculosis and is recommended for administration to infants.

Several new and better vaccines for the prevention of TB infection are being developed and have entered clinical trials in the United States. At present, health experts in the United States do not recommend the use of the vaccine for general use in this country because it makes the screening procedures for infected individuals more difficult. The TB skin test, also known as the tuberculin PPD test, is used for screening purposes and will show positive results in persons who currently has TB or were exposed or vaccinated in the past. The test is based on the fact that an encounter with M. tuberculosis produces a delayed hypersensitivity skin reaction (see Chapter 20, The Immune System) to certain components of the bacterium.

Haemophilus Infections

Many Haemophilus species are part of the normal flora in the upper airways of children and adults and most of them rarely cause disease. However, Haemophilus influenzae, a gram-negative coccobacillus (Figure 11.9), is a common cause of infection (bronchiolitis) in children and chronic bronchitis in adults, and occasionally meningitis.

H. influenzae and S. pneumoniae are sometimes isolated from the same individual. The transmission occurs by aerosols from an infected individual. Children are routinely and successfully vaccinated against Haemophilus influenzae type b, especially for the prevention of meningitis.

Klebsiella pneumoniae

Klebsiella pneumoniae is a gram-negative, encapsulated bacillus found in the normal flora of the mouth, skin, and intestines. It is an opportunistic pathogen that can cause bacterial pneumonia that is most often hospital-acquired (nosocomial) or occurs in nursing homes. Other people at risk are infants, older people, alcoholics, and people with chronic diseases, such as immune disorders. The infection is serious and persons are treated with antibiotics, supplemental oxygen, and intravenous fluids. Despite treatment the death toll ranges from 25% to 50% of infected patients.

Diphtheria

Diphtheria is caused by Corynebacterium diphtheriae, a facultative anaerobic, gram-positive bacillus (Figure 11.10), which attacks the throat and nose. It is an upper respiratory illness characterized by a sore throat, low-grade fever, and the formation of a pseudomembrane on the tonsils and pharynx. The formation of the pseudomembrane can cause life-threatening respiratory obstruction. It is a highly contagious disease easily spread by direct physical contact or aerosol secretions from an infected individual. Once the infection takes place the bacterium produces an exotoxin that can potentially spread via the bloodstream to other organs such as the heart and cause significant damage.

A vaccine is available and because of widespread routine childhood immunization, diphtheria is rare in the United States and in many other countries. It is reemerging in some parts of the world where immunization practices are not strictly followed. Other risk factors include crowded environments and poor hygiene.

Diphtheria is a medical emergency and delay in treatment can result in long-term heart disease. Treatment includes antitoxin to eliminate the toxin and antibiotics to eliminate the toxin-producing bacteria themselves. Recovery from the illness is slow and the death rate from diphtheria is 10% in infected patients.

Legionellosis

Legionellosis is an illness caused by Legionella pneumophila, a gram-negative bacillus found in water sources in the environment. The disease has two distinct forms:

Legionellosis is contracted when people inhale water mist containing the bacteria. Mist-producing devices that potentially can contain Legionella include air-conditioning systems in homes, workplaces, hospitals, or other public gathering places. Legionellosis is not spread from person to person, but only through contaminated water sources.

The symptoms of Pontiac fever include fever and muscle aches but do not include pneumonia, and infected persons usually recover within 2 to 5 days without requiring treatment. Persons with Legionnaire’s disease show more severe symptoms, including high fever, chills, and a cough that might or might not produce sputum. Other symptoms may include muscle aches, headache, tiredness, loss of appetite, and occasionally diarrhea. Chest x-rays often indicate signs of pneumonia. Distinguishing Legionnaire’s disease from other pneumonias is difficult on the basis of symptoms alone; specific tests are needed for a safe diagnosis. These tests include detecting Legionella in sputum and body fluids, or finding specific antibodies in the blood of the patient. Legionnaire’s disease can be treated with antibiotics.

Psittacosis

Psittacosis is an infection caused by Chlamydia psittaci, an obligate intracellular bacterium found in bird droppings. The illness is also known as parrot disease, parrot fever, and ornithosis. In birds the infection is referred to as avian chlamydiosis and Chlamydia is shed by infected birds through feces and nasal discharges, which can remain infectious for months. Psittacosis is a rare zoonotic infection and is spread from birds to humans. People at risk include bird owners, pet shop employees, workers in poultry-processing plants, and veterinarians. The symptoms of the disease include fever, chills, headache, muscle aches, dry cough, and often pneumonia. The incubation period after inhalation of dry bird secretions is 5 to 19 days. The infection is treated with antibiotics.

Inhalation Anthrax

Anthrax is an acute infectious disease caused by Bacillus anthracis, a gram-positive, spore-forming, facultative anaerobe (Figure 11.11), commonly found in wild and domestic vertebrates. The disease is zoonotic and can occur in humans if a person is exposed to an infected animal, tissue from an infected animal, or spores of the bacterium. The infection can be attained through the skin, by inhalation, or ingestion. There is no known transmission of anthrax from person to person. Symptoms of the disease vary depending on how it was acquired. Symptoms commonly occur within 7 days, but can take up to 60 days. Inhaling the spores only means that a person has been exposed to the disease; it does not mean that symptoms automatically appear, because the bacterial spores must germinate before the actual disease occurs. Once the spores germinate, they release several toxins that cause internal bleeding, swelling, and tissue necrosis. Anthrax spores can remain viable in the environment for 50 years.

The initial symptoms of anthrax when the bacterial spores are acquired through inhalation are similar to those of a common cold, including fever, chills, sweating, fatigue, malaise, headache, cough, shortness of breath, and some chest pain. After several days the symptoms usually progress to the second stage with fever, severe breathing problems, and shock. Cutaneous anthrax appears as a large, deep lesion on the skin, and gastrointestinal anthrax causes lesions in the intestinal tract, often with intestinal bleeding. Antibiotic therapy administered after known or suspected exposure can help prevent the disease. Several antibiotics are effective against anthrax; however, if the second stage has been reached, inhalation anthrax is usually fatal. Vaccination has been developed and is available to select U.S. military personnel, but not to the general public. Anthrax spores and their use in bioterrorism are discussed in Chapter 24 (Microorganisms in the Environment and Environmental Safety).

Q Fever

Q fever is a zoonotic disease caused by Coxiella burnetii, a gram-negative, coccobacillus that can form sporelike structures. The species is distributed globally and affects sheep, goats, cattle, dogs, cats, birds, rodents, and ticks. The organism can be excreted in milk, urine, and feces and is also shed in high numbers in the amniotic fluid and placenta during the birthing process. Coxiella is resistant to heat, drying, and common disinfectants, and therefore it can survive for long periods of time in the environment. Humans can acquire the infection by inhaling the organism from contaminated barnyard dust, birth fluids, and excreta of infected herd animals. Bites from infected ticks are another possible mode of transmission.

The susceptibility of humans to this disease is high and a small number of organisms appear to be causing the disease. The incubation time depends on the number of organisms that infect the patient, but symptoms usually occur within 2 to 3 weeks of exposure. Symptoms of acute Q fever include fever, headache, muscle pains, cough, chest pain during breathing, shortness of breath, jaundice, and clay-colored stools. Antibiotic treatment is most effective when started early. Chronic Q fever develops in persons who have not been treated effectively within 6 months of the initial exposure and management may require a combination of drugs and prolonged duration of treatment. Because of the nature of the agent (resistant to heat and drying) and human susceptibility to the organism it could be developed for use in biological warfare and, like anthrax, is considered a potential terrorist weapon.