Whooping cough
Whooping cough | |
---|---|
Other names | Pertussis, 100-day cough |
Antibiotics (if started early)[7] | |
Frequency | 16.3 million (2015)[8] |
Deaths | 58,700 (2015)[9] |
Whooping cough (
Pertussis is caused by the bacterium Bordetella pertussis, which is spread easily through the coughs and sneezes of an infected person.[4][12] People are infectious from the start of symptoms until about three weeks into the coughing fits.[7] Diagnosis is by collecting a sample from the back of the nose and throat.[5] This sample can then be tested either by culture or by polymerase chain reaction.[5]
Prevention is mainly by vaccination with the pertussis vaccine.[6] Initial immunization is recommended between six and eight weeks of age, with four doses to be given in the first two years of life.[13] Protection from pertussis decreases over time, so additional doses of vaccine are often recommended for older children and adults.[14] Vaccination during pregnancy is highly effective at protecting the infant from pertussis during their vulnerable early months of life, and is recommended in many countries.[15] Antibiotics may be used to prevent the disease in those who have been exposed and are at risk of severe disease.[16] In those with the disease, antibiotics are useful if started within three weeks of the initial symptoms, but otherwise have little effect in most people.[7] In pregnant women and children less than one year old, antibiotics are recommended within six weeks of symptom onset.[7] Antibiotics used include erythromycin, azithromycin, clarithromycin, or trimethoprim/sulfamethoxazole.[7] Evidence to support interventions for the cough, other than antibiotics, is poor.[17] About 50% of infected children less than a year old require hospitalization and nearly 0.5% (1 in 200) die.[1][2]
An estimated 16.3 million people worldwide were infected in 2015.
Signs and symptoms
The classic symptoms of pertussis are a
The illness usually starts with mild respiratory symptoms include mild coughing, sneezing, or a
This stage usually lasts two to eight weeks, or sometimes longer. A gradual transition then occurs to the convalescent stage, which usually lasts one to four weeks. This stage is marked by a decrease in paroxysms of coughing, although paroxysms may occur with subsequent respiratory infection for many months after the onset of pertussis.[20]
Symptoms of pertussis can be variable, especially between immunized and non-immunized people. Those that are immunized can present with a more mild infection; they may only have the paroxysmal cough for a couple of weeks, and it may lack the "whooping" characteristic.[21] Although immunized people have a milder form of the infection, they can spread the disease to others who are not immune.[21]
Incubation period
The time between exposure and the development of symptoms is on average 7–14 days (range 6–20 days),[22] rarely as long as 42 days.[23]
Cause
Pertussis is caused by the bacterium
Host species
Humans are the only host species of B. pertussis.[24] Outbreaks of whooping cough have been observed among chimpanzees in a zoo, and among wild gorillas; in both cases it is considered likely that the infection was acquired as a result of close contact with humans.[25][26] Several zoos have a long-standing custom of vaccinating their primates against whooping cough.[27]
Mechanism
After the bacteria are inhaled, they initially adhere to the
The bacteria secretes a number of toxins.
Diagnosis
Based on symptoms
A physician's overall impression is most effective in initially making the diagnosis.[32] Single factors are much less useful.[32] In adults with a cough of less than 8 weeks, vomiting after coughing or a "whoop" is supportive.[33] If there are no bouts of coughing or there is a fever the diagnosis is unlikely.[33] In children who have a cough of less than 4 weeks vomiting after coughing is somewhat supportive but not definitive.[33]
Lab tests
Methods used in laboratory diagnosis include culturing of nasopharyngeal swabs on a nutrient medium (Bordet–Gengou medium), polymerase chain reaction (PCR), direct fluorescent antibody (DFA), and serological methods (e.g. complement fixation test).[34] The bacteria can be recovered from the person only during the first three weeks of illness, rendering culturing and DFA useless after this period, although PCR may have some limited usefulness for an additional three weeks.
Serology may be used for adults and adolescents who have already been infected for several weeks to determine whether antibody against pertussis toxin or another virulence factor of B. pertussis is present at high levels in the blood of the person.[35]
Differential diagnosis
A similar, milder disease is caused by B. parapertussis.[36]
Prevention
The primary method of prevention for pertussis is vaccination.[37] Evidence is insufficient to determine the effectiveness of antibiotics in those who have been exposed, but are without symptoms.[38] Preventive antibiotics, however, are still frequently used in those who have been exposed and are at high risk of severe disease (such as infants).[6]
Vaccine
Pertussis vaccines are effective at preventing illness[39] and are recommended for routine use by the World Health Organization[40] and the United States Centers for Disease Control and Prevention.[41] The vaccine saved an estimated half a million lives in 2002.[40]
The multicomponent
Immunization does not confer lifelong immunity; a 2011 CDC study indicated that protection may only last three to six years. This covers childhood, which is the time of greatest exposure and greatest risk of death from pertussis.[19][44]
An effect of widespread immunization on society has been the shift of reported infections from children aged 1–9 years to infants, adolescents, and adults, with adolescents and adults acting as reservoirs for B. pertussis and infecting infants who have had fewer than three doses of vaccine.[45]
Infection induces incomplete
Some studies have suggested that while acellular pertussis vaccines are effective at preventing the disease, they have a limited impact on infection and transmission, meaning that vaccinated people could spread pertussis even though they may have only mild symptoms or none at all.[49][50] Pertussis infection in these persons may be asymptomatic, or present as illness ranging from a mild cough to classic pertussis with persistent cough (i.e., lasting more than 7 days). Even though the disease may be milder in older persons, those who are infected may transmit the disease to other susceptible persons, including unimmunized or incompletely immunized infants. Older persons are often found to have the first case in a household with multiple pertussis cases, and are often the source of infection for children.[20]
Treatment
The antibiotics
A reasonable guideline is to treat people age >1 year within 3 weeks of cough onset and infants age <1 year and pregnant women within 6 weeks of cough onset. If the person is diagnosed late, antibiotics will not alter the course of the illness, and even without antibiotics, they should no longer be spreading pertussis.[6] When used early, antibiotics decrease the duration of infectiousness, and thus prevent spread.[6] Short-term antibiotics (azithromycin for 3–5 days) are as effective as long-term treatment (erythromycin 10–14 days) in eliminating B. pertussis with fewer and less severe side effects.[38]
People with pertussis are most infectious during the first two weeks following the onset of symptoms.[51]
Effective treatments of the cough associated with this condition have not been developed.[52] The use of over the counter cough medications is discouraged and has not been found helpful.[21]
Prognosis
While most healthy older children and adults fully recover, infection in newborns is particularly severe. Pertussis is fatal in an estimated 0.5% of US infants under one year of age.[53] First-year infants are also more likely to develop complications, such as: apneas (31%), pneumonia (12%), seizures (0.6%) and encephalopathy (0.15%).[53] This may be due to the ability of the bacterium to suppress the immune system.[54]
Epidemiology
Pertussis is endemic worldwide. More than 151,000 cases were reported globally during 2018.[55] However not all cases are reported or correctly diagnosed, especially in developing countries. Pertussis is one of the leading causes of vaccine-preventable deaths worldwide.[56] A study in 2017 estimated the global burden of the disease to be 24 million cases per year with 160,000 deaths among young children, with about 90% of all cases occurring in developing countries.[57][56]
Before vaccines, an average of 178,171 cases was reported in the U.S., with peaks reported every two to five years; more than 93% of reported cases occurred in children under 10 years of age. The actual incidence was likely much higher. After vaccinations were introduced in the 1940s, pertussis incidence fell dramatically to approximately 1,000 by 1976. Incidence rates have increased since 1980. In 2015, 20,762 people were reported to have been infected in the United States.[58] Pertussis is the only vaccine-preventable disease that is associated with increasing deaths in the U.S. The number of deaths increased from four in 1996 to 17 in 2001, almost all of which were infants under one year.[59] In the U.S. pertussis in adults has increased significantly since about 2004.[60]
Epidemics of the disease occur cyclically, every three to 5 years, both in areas with vaccination programs and those without.[61] Over time, immunity declines in those who have either been vaccinated or have recovered from infection.[62] In addition, infants are born who are susceptible to infection. An epidemic can occur once herd immunity reduces below decreases below a certain level.[63] It is also possible that the bacterium is evolving to evade vaccine-induced immunity.[64][61]
History
Discovery
B. pertussis was discovered in 1906 by Jules Bordet and Octave Gengou, who also developed the first serology and vaccine. Efforts to develop an inactivated whole-cell vaccine began soon after B. pertussis was cultured that year. In the 1920s, Louis W. Sauer developed a weak vaccine for whooping cough at Evanston Hospital (Evanston, IL). In 1925 Danish physician Thorvald Madsen was the first to test a whole-cell vaccine on a wide scale.[65] Madsen used the vaccine to control outbreaks in the Faroe Islands in the North Sea.
Vaccine
In 1932, an outbreak of whooping cough hit
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External links
- Pertussis at Todar's Online Textbook of Bacteriology
- PBS NOVA – Vaccines: Calling The Shots
- "Whooping Cough". MedlinePlus. U.S. National Library of Medicine.