The acute respiratory infections (ARI) are the commonest causes of ill health in the world. WHO have estimated that there are 14-15 million deaths a year in children under 5 years of age and one-third of these are due to ARI, yet despite their importance, they are a poorly defined group of diseases. They include the common cold, influenza, pneumonia, bronchitis and a number of other infections. They can be separated by clinical criteria, but it is the differing response of the individual to the organism that determines the clinical severity and management. A mild infection from an upper respiratory tract infection in one person may develop in another to a life-threatening attack of pneumonia. It is, therefore, not only the organism that determines the disease, but also the patient's response to the organism.
Organisms A number of different organisms have been implicated including Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, influenza, rhino-viruses, adenoviruses, metapneumovirus and respiratory syncytial virus (RSV). Viruses are of a wide range, with each species having a number of serotypes, with new ones appearing from time to time. However, the most important cause is S. pneumoniae or the pneumococcus or H. influenzae. The host defends him or herself by producing an appropriate immune response, but because of the large number of serotypes, it is a continuous process. Infection will cause illness in some people, but not in others who have developed an immune response to the specific organism or an antigenically similar serotype. New antigenic mutations, as occur in influenza, can cause epidemic or pandemic spread because no prior contact with the new variant has been made.
Clinical features ARIs are divided into upper and lower ARIs, the former producing a running nose, sneezing and headache, while the main symptoms of lower respiratory tract infection are cough, shortness of breath and inward drawing of the bony structure of the lower chest wall during inspiration, which is called chest indrawing. Both are generally accompanied by fever. The main pathological feature is pneumonia, which can either be lobar or bronchial. In lobar pneumonia, one or more well-defined lobes of the lung are involved, whereas in bronchial pneumonia the condition is widespread. The causes of pneumonia are listed in Table 13.1.
Diagnosis Identifying the organism by culture of the sputum can be attempted where facilities permit, but in most developing countries, ARI will be diagnosed on clinical criteria.
Transmission is by coughing out a large number of organisms in a fine aerosol of droplets, which are either breathed in, enter via the conjunctiva or are swallowed from fingers or utensils. Susceptibility and response are determined by host factors, some of which are listed below:
1. Age. Young children develop obstructive diseases, such as croup (laryngo-tracheo-bronchitis) and bronchiolitis. Tonsillitis is commonest in school age, whereas influenza and pneumonia are important causes of death in the elderly. In young children, mortality is inversely related to age.
2. Portal of entry. Volunteers have been more easily infected by some organisms applied to the conjunctiva than through the nasopharynx.
3. Nutrition. Low birth weight and malnourished children have a higher morbidity and mortality. Certain nutritional deficiencies, such as deficiencies of vitamin A and zinc, contribute to the development of a more severe disease and higher death rate.
4. Socio-economic. ARI is a disease of poverty with higher incidence in lower socioeconomic groups and those that live in urban slums. Higher rates of lower respiratory disease have been found with increasing family size. Much of the reason for this increase appears to be due to increased contact and agglomeration as shown by children attending day care facilities or school where infection occurs irrespective of social class.
5. Air pollution. A correlation with domestic air pollution has been shown in South Africa and Nepal. Passive smoking may affect pulmonary function and make the child more susceptible to infection as well as influence the child to become a smoker.
6. Climate. More respiratory infections are found in the cooler parts of the world or in the higher altitude regions of the tropics. There is a distinct seasonal effect in many countries, with more respiratory infections in the winter. However, cold alone is not a causative factor. 'Cold' derives its name from the belief that becoming chilled or standing in a draught is responsible, but when volunteers are subjected to these stresses and inoculated with rhinoviruses, they develop no more 'colds' than controls.
7. Other infections. Any infection, which causes damage to the respiratory mucosa, will allow a mild infecting organism to progress to more serious consequences. The most important of these diseases is measles, with post-measles pneumonia being particularly common.
Incubation period This varies with the organism, but in most cases is 1-3 days.
Period of communicability Variable; for the entire period of any respiratory symptoms.
Occurrence and distribution Worldwide, the most important cause of death in children in developing countries.
Treatment The first line of action is to assess the severity of illness and give treatment. This is supportive therapy for mild infec tions and the active administration of antibiotics to the severe case. The mild infection is best treated at home and kept away from sources of other infection, which may cause more serious disease, while the severe case requires early treatment to prevent complications and death. In children, the respiratory rate and chest indrawing are used to decide management:
• Mild cases, with a respiratory rate of less than 40 breaths/min in children of age 2-12 months and 50 breaths/min in the children of age 1-5 years, are treated at home with supportive therapy. The mother should be encouraged to nurse her child, giving it plenty of fluids (breast-feeding or from a cup), regular feeding, cleaning the nose, maintaining it at a comfortable temperature and avoiding contact with others.
• Moderate cases, with a respiratory rate of over 40 breaths/min in under-1-year-olds and 50 breaths/min in children 1-5 years old, but with no chest indrawing, should be given antibiotics (oral cotrimoxazole (4 mg/kg twice daily), oral amoxycillin (15mg/kg three times a day) or intramuscular penicillin G) and nursed at home.
• Severe cases, with chest indrawing, cyanosis or too sick to feed, must be admitted as in-patients and given active support as well as treatment with antibiotics.
Control and prevention The first step in management of a child with ARI is to separate the mild from the moderate and to treat the moderate and severe. The essence is speed and active treatment. This can easily be taught at the primary health care level. The mother can be educated on the management of her child with a mild infection and when to refer. It is the delay in referral and treatment that will allow a moderate case to become severe and the severe to die.
The village health worker can identify and treat the mild or moderate case of ARI using simple diagnostic criteria and a standard treatment protocol. Measuring the respiratory rate and knowing which action to take are the most important aspects. Training and supervision of primary health care workers is a priority in the management of ARI.
Preventive actions that can be undertaken are listed below:
• Reduce contact. ARIs are just as common in industrialized countries as they are in developing countries, but infant deaths from respiratory infections in the former have declined. The reason would appear to be due to smaller families and greater birth intervals, permitting increased individual care of children and better nutrition. The child is reared at home and does not need to be carried round where it is exposed at a very young age to infecting organisms.
• Good nutrition. Well-nourished children are in a stronger position to defend themselves against any infection. Encourage breast-feeding, especially during early stages of illness. Providing additional nutritional support to children with measles can prevent them developing post-measles pneumonia.
• Health education. Teach people to cough away from others, cover the mouth when coughing, not to spit or smoke and provide proper ventilation for smoke and fumes.
• Vaccination of childhood infections. The danger of developing pneumonia after measles is a serious problem, so prevention of measles will reduce the severe forms of ARI. Indeed, measles vaccination is perhaps the single most effective preventive method (Section 12.2). Vaccination for H. influenzae is now recommended by WHO in routine childhood immunization programmes. Pertussis, diphtheria and BCG vaccination should also be encouraged.
• Other vaccines. Influenza vaccine is prepared annually according to the expected strain of influenza and should be given to those at risk (e.g. immunocompromised and those with chronic respiratory infections) if facilities allow. The polysacchar-ide pneumococcal vaccine is not recommended in routine childhood vaccination programmes, but could be used in special circumstances, such as for sple-
nectomized children and the immuno-deficient. However, the new conjugate pneumococcal vaccine shows promise in children under 2 years of age and is likely to be included in childhood vaccination programmes if sufficient supplies can be made available. Vaccines against RSV, parainfluenza and the adenoviruses are in preparation.
Surveillance Measles generally occurs as seasonal epidemics, which can be forecasted and top-up vaccination given (Section 12.2). Influenza is normally pandemic with warning given of strain of organism and vaccine composition, allowing sufficient time for persons at risk to be protected.
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