Indian J Pediatr 1987; 54:153-160

Epidemiology of acute respiratory infections Jai P. Narain National Institute of Communicable Diseases, Delhi Acute respiratory infections (ARI) constitute a group of conditions caused by a variety of pathogens including bacteria and viruses. The group includes influenza, sinusitis, acute otids media, nasopharyngitis, tonsillitis, epiglottitis, laryngitis, tracheitis, acute bronchitis, bronchiolitis and pneumonia. Others like measles, diphtheria, whooping cough and childhood tuberculosis are preventable with immunizations and have been included in the expanded programme of immunization (EPI). ARI, and diarrheal diseases are the commonest and most significant health problems in developing countries, and with malnutrition as an associated or underlying cause constitute the principal causes of preventable mortality particularly among children),2 A national control programme for diarrheal diseases has been launched, but so far there has been no such commitment with regard to ARI. Considering the magnitude of A RI as a health problem, it is time for developing countries to start thinking of a national control programme on ARI.

Magnitude of the problem Global. It is not generally recognised that ARI is one of the most important Reprint requests : Dr. Jai P. Narain, Assistant Director, National Institute of Communicable Diseases, 22, Sham Nath Marg, New Delhi 110054.

causes of mortality in the world. 3 However, data from WHO from 88 countries representing one fourth of the world's population indicate that there are over 6,66,000 deaths from AR[ every year (Table I). On the assumption that mortality rates in non-reporting countries are similar to these 88 countries, it is estimated that about 2.2 million deaths from ARI occur throughout the world every year. 4 The mortality rates per 100,000 population are high in Africa (103-2) and Asia (87.2) compared to North America (30.5). In developing countries, the rates are considerably higher among children under the age of one year followed by those in 1-4 years age group. In some the rates are as high as 1000 per 100,000 live births or more (Table II). Among children in 1-4 years age group, these rates vary from 467 in Africa and 204 in Asia to 8 per 100,000 in North America and Australia. Accordingly, considerable differences exist in the proportion of deaths from ARI to deaths from all causes between different continents and various age groups.2 While this is uniformly high in children residing in Africa and Asia, it is highest in the 1-4 years age group.

National ARI accounts for 14-3~o of deaths during infancy and 15.9Yo of deaths between 1-5 years of age. 5 In pediatric age 153

154 THE 1NDIAN JOURNAL OF PEDIATRICS Table 1. Mortality from acute respiratory disease (AR1) in the world, 1970-73 Continent

Africa America Asia Europe Oceania Total

Population in thousand 77,420 40I ,573 227,310 462,936 16,893 1186,134

Deaths Per due to 100,000 ARI population 79,887 103-2 244,926 61- 0 127,847 84" 3 209,654 45" 3 4,412 26-1 666,726 56" 2

TabLe 2. Morlality rate per 100,000 population from ARI, 1970-73 Continent

Infants

Children 1-4 yr

Children 5-14 yr

Africa N. America Asian LDC Europe Oceania Total

1454"1 146"3 1242.4 390.3 177.6 762.2

467-0 8"0 204.1 15-~3 9" 3 10I'3

21-6 1"5 23.4 2.1 1"2 8.4

group, 20-24~ of deaths are reportedly attributable to acute lower respiratory infections. 6 This proportion is higher than that due to diarrheal diseases. Community based studies also indicate that A R I is a significant cause of mortality and account for 20-29~o of all deaths, v-9 Since the mortality rate from A R I in our country is expected to be as high as that of most Asian countries (84.2 per 100,000 population), it is estimated that each year at least 6-3 lakh persons die in India because of ARI. That acute respiratory illnesses in developing countries are of severe and life-threatening nature can be seen from A R I associated case fatality rates which among hospitalised patients is as high as

Vol. 54, No. 2 5-10~o. 10 In communities where diagnostic and treatment facilities are not available, rates are expected to be even higher. Conditions that are primarily responsible for childhood mortality are pneumonia, bronchiolitis and acute obstructive laryngitis. Pneumonia (bacterial and viral) alone accounts for 75~o of deaths from ARI. In most developing countries, communicable disease morbidity data at national level are not available because of lack of surveillance mechanism for collection of such information. In India some morbidity data on various communicable diseases are being passively collected by the Central Bureau of Health Intelligence (CBHI). According to C B H I data for 1983, there were at least 3.3 million cases of A R I reported as influenza, diphtheria, whooping cough and measles. 11 This does not, however, reflect the true picture as these data are primarily institution based and represent considerable under-reporting of information. Community-based studies show that A R I is indeed very c o m m o n and constitutes a major cause of childhood morbidity. On an average, a child in urban area during first five years of life may suffer from 5-8 episodes of A R I per year.12,13 In rural areas the reported incidence per child is lower (1-3 episodes per year).14,15 These figures are comparable to those seen in Western countries 16 (Table III). The difference, however, lies in the predisposition to and severity of acute lower respiratory tract illness, in particular pneumonia (Table IV). While annual incidence of pneumonia among children below five years of age in the U.S.A. is 30-40 per 1000 children, the rate in rural Punjab has been 94 and among Navajo Indians 91"2 per 10130 during first five years of life. 17-19

NARA1N: EPIDEMIOLOGY OF ARI

155

Table III. Frequency of ARI in urban and rural areas Area

Study years

No. of children

No. of episodes/yr Infants

Urban New Delhi Vellore Seattle, USA Rural Punjab Bangladesh

1962-67 1965-67 1969-72

7493 135 390

1975-76 1978-79

120 197

I-2

3-5

4.5

5" 3 7- 3 5.0

4" 8 6- 2 4" 8

2.3

2.5 (0-14 years) 2.5

2.3

5.6

Table IV. Annual incidence of pneumonia in children

Place

Year of study

Seattle, USA New Mexico and Arizona, USA Punjab, India

This can probably be explained by the presence of various host and environmental factors which predispose a child to lower respiratory infections. The magnitude of A R I morbidity and its impact on the health services can be measured by the proportion of outpatient attendance due to ARI. As high as 20-40 per cent of children brought to outpatients and 12-35~0 of children admitted to hospital may have ARI.20, 21 In health centres too an equally high proportion of patients are seen for respiratory complaints. 22

Descriptive epidemiology A R I most commonly occur in the first year of life, followed by 1,4 years

1966-73 1972-73 1970-73

No. Of pneumonia/1000 children Infants

1-4 yr

Total

-291- 4 --

36.0 39" 9 --

30"0 91" 2 94-1

age group. In a study in urban Delhi, the incidence was 81 per 1000 months during first year of life and then decreased to 68, 67, 56 and 31 per 1000 months during subsequent f our years. 23 Other studies in urban areas show similar pattern.24, z5 In rural Haryana, however, an opposite picture was seen with attack rate of 2.2 per year during infancy, increasing to 3.9 per year during 13-24 months and 42 per year in 25-36 months of age. l0 The reasoa for such a difference between urban and rural A R I morbidity remains unclarified. In both developed and developing countries respiratory infections usually occur more frequently during cold weather than in any other season; twice or three times as common in winter as in summer. 26

156 THE INDIAN JOURNAL OF PEDIATRICS Most studies in North India also show that incidence of ARI is highest during winter months. 23-2s In Calcutta, however, peak incidence was seen before and during the monsoon season.27 Respiratory infections tend to affect more frequently males than females. The ratio is about 1.7 to 1. The difference may partly be due to preferential treatment to male children who when sick are more likely to be brought to hospital or a health care unit. Etiology and transmission Among etiological agents responsible for ARI are viruses, bacteria, mycoplasma etc. Most frequent viral agents include the respiratory syncytial viruses (RSV), parainfluenza and adenoviruses. Although viral agents are generally associated with acute upper respiratory illness, RSV may cause life-threatening bronchiolitis particularly in infants while parainfluenza is responsible for acute obstructive laryngitis (croup). Bacterial agents responsible f o r ARI are

Streptococcus pneumoniae, Haemopkilus influenzae, Streptococcus pyogenes etc. In bacterial pneumonias as a complication of measles Staphylococi are commonly found. Fortunately in patients with serious lower respiratory tract infections in developing countries, bacteria have been the most frequently isolated organisms28, 29. This differs from developed countries where viruses have been the most common organisms. Laboratory diagnosis of ARI, however, presents a problem. In a high proportion (50~o) of cases, no pathological agents are found. In addition, majority of healthy children may carry S. pneumoniae. Therefore, etiological significance of isolation of an agent is often difficult to interpret.

Vol. 54, No. 2 Transmission of majority of respiratory pathogens occurs from person to person through respiratory and nasopharyngeal secretions. Studies emphasise the importance of home in the person to person spread.30, 31 Often ARI is introduced into the family by school age children and spread to others is influenced by the degree of overcrowding. Spread due to direct hand contact and thence by self-inoculation of nose or eyes has also been demonstrated. 32 In ARI of bacterial etiology, a person responsible for transmitting infection is likely to have had an antecedent upper respiratory illness probably of viral etiology more than at any other time. 33 This suggests that enhanced production of respiratory secretions during viral cold may play a role in transfer of bacterial agents to susceptible persons. It is also possible that S. pneumoniae may migrate from pharynx to nose in persons with cold, an event evidenced by an increased rate of bacterial recovery from nasal cultures during respiratory illness. Risk factors

ARI associated mortality in developed countries declined dramatically during the past few decades because of widespread use of antibiotic therapy, immunization with DPT, measles and influenza vaccines, improved health care management and adequate nutrition for infants and children. In developing countries, on the other hand, no such change has been witnessed as the standard of living continues to be associated with factors which increase ~he risk of severe respiratory infections in children. One of the most important factors that predispose a child to severe ARI is low birth weight. The incidence of mortality due to ARI during the first year of

NARAIN: EPIDEMIOLOGYOF ARI life is much higher in low birth weight infants than those weighing > 2500 gm or more at birth. Pneumoniae are the greatest cause of death in these children. Since between 20-40% of newborns in India have low birth weight, a high proportion of these infants once infected are prone to death from pneumonia. In a study in England, mortality per 1000 live births during infancy was 26.4 among low weight children compared to 6.8 for children with birth weight of over 2500 gin.34 Synergistic action between malnutrition and infection is well recognised as the presence of one predisposes and aggravates the other. In a malnourished child, there is significant impairment in immunity particularly of cellular type which increases susceptibility to ARI and secondary infection. Although no correlation is generally seen between malnutrition and overall incidence of ARI morbidity a malnourished child tends to have severe illness. The average duration of illness in a malnourished child is significantly longer, bronchitis occurs three times and pneumonia nineteen times more frequently compared with normal children. 35 Adverse effect of malnutrition can best be seen in measles. 36 Four respiratory illnesses such as measles, diphtheria, whooping cough and childhood tuberculosis are preventable by immunization. The lack of childhood immunization history against these, therefore, constitutes an important risk factor. Pneumonia is a common complication associated with measles and whooping cough. Many antecedent viral infections seem to play an important role in the invasion of the human host by bacterial pathogens present in the Oropharynx 33. These act

157 by impairing a child's immune status and by damaging bronchial epithelium and thereby preventing clearing of bacterial agentS. Environmental factors

Both indoor and outdoor air pollution can be associated with ARI. In a prospective study in Bombay, a higher proportion (26%) of persons having common cold were from more environmentally polluted areas compared to those in other areas (11-I4%). 3v A study undertaken in England showed that air pollution was associated with an increased incidence of acute lower respiratory infection.3s Severe lower respiratory infection occurred much more frequently in big cities with high pollution levels than in rural areas and small towns, although overall incidence of ARI was no significantly different. The inhalants in polluted air cause damage to tracheobronchial mucosa and bring about ciliary paralysis which might increase susceptibility to severe infection. Data from developed countries indicate that passive smoking may predispose a child to respiratory illness. 39 Children of parents who smoke in the house have been found to have increased risk of bronchitis and pneumonia in comparison to children of non-smoking parents.40 The risk is much greater if both parents are smokers than when either of them is a smoker. The passive exposure to smoke in childhood has an important bearing on the development of respiratory function which in turn may predispose a child to increased risk from environmental agents later in life. Evidence from developing countries on the contribution of passive smoking on the incidence and severity of ARI is at present lacking.

158 THE INDIAN JOURNAL OF PEDIATRICS Although use of gas for cooking has been identified as a risk factor, 41 the possible effects of polllution .from biomass fuels on incidence of ARI have not yet been fully investigated. There is however some evidence to suggest that exposure to burning biomass fuel common in many developing countries may play an importantrole in the etiology of ARI. In South Africa, among 132 infants with severe lower respiratory infection studied, 70~ of the cases compared to only 33~o of control infants had a history of heavy exposure to smoke from cooking and heating fires. 42 Further epidemiological studies are needed to clarify inter-relationship between the fuels used in cooking and heating purposes and possibility of ARI in children. Social factors Among factors that play a crucial role in the spread of infection is overcrowding in the home. Of several social factors including range of outside contact, dampness and ventilation in the house, general level of hygiene etc. examined, overcrowding in the house (five members in one or two rooms) was found to be the one which was intimately related to the high incidence of respiratory illness. 31 In conditions of continued close contact in the more crowded families, higher secondary attack rates are seen. 33 Several studies in India show that there is a greater likelihood of ARI in larger families than those with fewer family members.7, 2~ Like in many other infections, breast feeding protects also against severe respiratory infections. Humoral antibodies and other host resistance factors present in human milk play a crucial role against both viral and bacterial agents. In Ambala

Vol. 54, No. 2 (Haryana) infants who were breastfed had significantly lower attack rates than those who were given bottle feed. 43 With the practice of breast feeding, the risk of admission to hospital for respiratory virus infections have been brought down by half. 44 Other inter-related social risk factors which could possibly play a role in ARI are condition of housing, personal

hygiene, educational background of mother and non-utilisation of heatlh care facilities. The relative importance of each o f these factors to the incidence and severity of ARI is yet to be evaluated. Recommendations Studies are needed to assess the epidemiology of ARI in each country and the factors responsible for the higher incidence and severity of the disease. Studies to evaluate impact of case management protocols and of EPI on ARI associated mortality may be carried out. Emphasis should be placed on etiological diagnosis using rapid diagnostic techniques to complement epidemiological data. Uniform case definition based on severity rather than anatomical location needs to be developed and field tested. This is expected to have ARI management implications for simplicity and feasibility of its application under the primary health care approach. Besides determining the pathogens responsible for severe ARI, there is need for a mechanism of continuous monitoring of bacterial susceptibility to antimicrobials in the community. Multicentric studies at different areas with varying grades of environmental pollution may be useful to assess the role of outdoor air pollution on incidence of ARI.

NARAIN : E P I D E M I O L O G Y OF AR1 References

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