Epidemiological measures: application and interpretation in real-life scenarios according to epidemiological study designs

Frequency, association and impact measures are key concepts in clinical epidemiology; however, it has been found that a considerable proportion of health students and professionals have no knowledge of how to use or interpret them when reading a scientific paper or conducting research. This article aims to explain the main epidemiological measures, how they are used, derived and interpreted. They are approached from the perspective of each of the most frequently used types of primary quantitative research studies (randomized clinical trials, cohort studies, case-control estudies and cross-sectional studies) in order to provide the reader with the context in which they are used. Moreover, the process for calculating and interpreting each result in a real setting is explained using clinical examples for a better understanding of these concepts and in order to prevent their use from becoming just a mechanical or repetitive exercise.

Las medidas de frecuencia, asociación e impacto son conceptos fundamentales de la epidemiología clínica; sin embargo, se ha encontrado que una parte considerable de los estudiantes y de los profesionales en el área de la salud no sabe cómo usarlas ni cómo interpretarlas al leer un texto científico o al hacer una investigación. Este artículo busca explicar las principales medidas epidemiológicas, cuándo se usan, cómo se obtienen y cómo se interpretan. Se abordan desde cada tipo de estudios primarios más frecuentemente utilizados cuando se realizan investigaciones cuantitativas (ensayos clínicos aleatorizados, estudios de cohorte, casos y controles y estudios de corte transversal), con el fin de darle al lector el contexto en el cual se usan. Además, mediante ejemplos clínicos, se explica el proceso para calcular e interpretar cada resultado en un escenario real, con el fin de lograr una mayor comprensión de estos conceptos y de que su uso no sea un ejercicio mecánico o de repetición.

Chest physiotherapy for acute bronchiolitis in paediatric patients between 0 and 24 months old.

BACKGROUND: Acute bronchiolitis is the leading cause of medical emergencies during winter months in infants younger than 24 months old. Chest physiotherapy is sometimes used to assist infants in the clearance of secretions in order to decrease ventilatory effort. This is an update of a Cochrane Review first published in 2005 and updated in 2006, 2012, and 2016. OBJECTIVES: To determine the efficacy of chest physiotherapy in infants younger than 24 months old with acute bronchiolitis. A secondary objective was to determine the efficacy of different techniques of chest physiotherapy (vibration and percussion, passive exhalation, or instrumental). SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, CINAHL, LILACS, Web of Science, PEDro (October 2011 to 20 April 2022), and two trials registers (5 April 2022). SELECTION CRITERIA: Randomised controlled trials (RCTs) in which chest physiotherapy was compared to control (conventional medical care with no physiotherapy intervention) or other respiratory physiotherapy techniques in infants younger than 24 months old with bronchiolitis. DATA COLLECTION AND ANALYSIS: We used standard methodological procedures expected by Cochrane. MAIN RESULTS: Our update of the searches dated 20 April 2022 identified five new RCTs with 430 participants. We included a total of 17 RCTs (1679 participants) comparing chest physiotherapy with no intervention or comparing different types of physiotherapy. Five trials (246 participants) assessed percussion and vibration techniques plus postural drainage (conventional chest physiotherapy), and 12 trials (1433 participants) assessed different passive flow-oriented expiratory techniques, of which three trials (628 participants) assessed forced expiratory techniques, and nine trials (805 participants) assessed slow expiratory techniques. In the slow expiratory subgroup, two trials (78 participants) compared the technique with instrumental physiotherapy techniques, and two recent trials (116 participants) combined slow expiratory techniques with rhinopharyngeal retrograde technique (RRT). One trial used RRT alone as the main component of the physiotherapy intervention. Clinical severity was mild in one trial, severe in four trials, moderate in six trials, and mild to moderate in five trials. One study did not report clinical severity. Two trials were performed on non-hospitalised participants. Overall risk of bias was high in six trials, unclear in five, and low in six trials. The analyses showed no effects of conventional techniques on change in bronchiolitis severity status, respiratory parameters, hours with oxygen supplementation, or length of hospital stay (5 trials, 246 participants).  Regarding instrumental techniques (2 trials, 80 participants), one trial observed similar results in bronchiolitis severity status when comparing slow expiration to instrumental techniques (mean difference 0.10, 95% confidence interval (C) -0.17 to 0.37).  Forced passive expiratory techniques failed to show an effect on bronchiolitis severity in time to recovery (2 trials, 509 participants; high-certainty evidence) and time to clinical stability (1 trial, 99 participants; high-certainty evidence) in infants with severe bronchiolitis. Important adverse effects were reported with the use of forced expiratory techniques.  Regarding slow expiratory techniques, a mild to moderate improvement was observed in bronchiolitis severity score (standardised mean difference -0.43, 95% CI -0.73 to -0.13; I2 = 55%; 7 trials, 434 participants; low-certainty evidence). Also, in one trial an improvement in time to recovery was observed with the use of slow expiratory techniques. No benefit was observed in length of hospital stay, except for one trial which showed a one-day reduction. No effects were shown or reported for other clinical outcomes such as duration on oxygen supplementation, use of bronchodilators, or parents' impression of physiotherapy benefit. AUTHORS' CONCLUSIONS: We found low-certainty evidence that passive slow expiratory technique may result in a mild to moderate improvement in bronchiolitis severity when compared to control. This evidence comes mostly from infants with moderately acute bronchiolitis treated in hospital. The evidence was limited with regard to infants with severe bronchiolitis and those with moderately severe bronchiolitis treated in ambulatory settings. We found high-certainty evidence that conventional techniques and forced expiratory techniques result in no difference in bronchiolitis severity or any other outcome. We found high-certainty evidence that forced expiratory techniques in infants with severe bronchiolitis do not improve their health status and can lead to severe adverse effects. Currently, the evidence regarding new physiotherapy techniques such as RRT or instrumental physiotherapy is scarce, and further trials are needed to determine their effects and potential for use in infants with moderate bronchiolitis, as well as the potential additional effect of RRT when combined with slow passive expiratory techniques. Finally, the effectiveness of combining chest physiotherapy with hypertonic saline should also be investigated.

Exposure to armed conflict as a factor associated with very low birth weight: Case-control population study.

OBJECTIVE: To determine the association between armed conflict and very low birth wright (VLBW), which is a multifactorial etiology public health problem that includes aspects of poverty and violence. METHODS: Case-control population study matched by year of delivery conducted in Cauca, Colombia, between 2010 and 2016. Cases of VLBW, with weights between 500 and 1499 g and controls weighing between 2500 and 3999 g. Cases and controls were identified through the vital statistics registry, and exposure was determined using a multidimensional index designed by the Colombian State. Multiple gestations were excluded. Conditional logistic regression for matched data was used, adjusting for confounding variables. RESULTS: Overall, 7068 matched participants (1767 cases and 5301 controls) were included. Cases and controls had similar baseline characteristics. Participants were predominantly women in the second and third decades of life, 3222 (46%) were exposed to armed conflict, and 1902 (27%) were of African-Colombian or indigenous ethnicity. Maternal exposure to armed conflict significantly increased the odds of VLBW among women with rural birth (adjusted odds ratio [aOR] 3.86, 95% confidence interval [CI] 2.74-5.45) and inadequate prenatal care (aOR 10.38, 95% CI 8.20-13.12). CONCLUSION: Exposure to armed conflict increases the odds of VLBW neonates. This factor needs to be considered in prenatal care.

Chest physiotherapy for acute bronchiolitis in paediatric patients between 0 and 24 months old.

BACKGROUND: This Cochrane review was first published in 2005 and updated in 2007, 2012 and now 2015. Acute bronchiolitis is the leading cause of medical emergencies during winter in children younger than two years of age. Chest physiotherapy is sometimes used to assist infants in the clearance of secretions in order to decrease ventilatory effort. OBJECTIVES: To determine the efficacy of chest physiotherapy in infants aged less than 24 months old with acute bronchiolitis. A secondary objective was to determine the efficacy of different techniques of chest physiotherapy (for example, vibration and percussion and passive forced exhalation). SEARCH METHODS: We searched CENTRAL (2015, Issue 9) (accessed 8 July 2015), MEDLINE (1966 to July 2015), MEDLINE in-process and other non-indexed citations (July 2015), EMBASE (1990 to July 2015), CINAHL (1982 to July 2015), LILACS (1985 to July 2015), Web of Science (1985 to July 2015) and Pedro (1929 to July 2015). SELECTION CRITERIA: Randomised controlled trials (RCTs) in which chest physiotherapy was compared against no intervention or against another type of physiotherapy in bronchiolitis patients younger than 24 months of age. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data. Primary outcomes were change in the severity status of bronchiolitis and time to recovery. Secondary outcomes were respiratory parameters, duration of oxygen supplementation, length of hospital stay, use of bronchodilators and steroids, adverse events and parents' impression of physiotherapy benefit. No pooling of data was possible. MAIN RESULTS: We included 12 RCTs (1249 participants), three more than the previous Cochrane review, comparing physiotherapy with no intervention. Five trials (246 participants) evaluated conventional techniques (vibration and percussion plus postural drainage), and seven trials (1003 participants) evaluated passive flow-oriented expiratory techniques: slow passive expiratory techniques in four trials, and forced passive expiratory techniques in three trials.Conventional techniques failed to show a benefit in the primary outcome of change in severity status of bronchiolitis measured by means of clinical scores (five trials, 241 participants analysed). Safety of conventional techniques has been studied only anecdotally, with one case of atelectasis, the collapse or closure of the lung resulting in reduced or absent gas exchange, reported in the control arm of one trial.Slow passive expiratory techniques failed to show a benefit in the primary outcomes of severity status of bronchiolitis and in time to recovery (low quality of evidence). Three trials analysing 286 participants measured severity of bronchiolitis through clinical scores, with no significant differences between groups in any of these trials, conducted in patients with moderate and severe disease. Only one trial observed a transient significant small improvement in the Wang clinical score immediately after the intervention in patients with moderate severity of disease. There is very low quality evidence that slow passive expiratory techniques seem to be safe, as two studies (256 participants) reported that no adverse effects were observed.Forced passive expiratory techniques failed to show an effect on severity of bronchiolitis in terms of time to recovery (two trials, 509 participants) and time to clinical stability (one trial, 99 participants analysed). This evidence is of high quality and corresponds to patients with severe bronchiolitis. Furthermore, there is also high quality evidence that these techniques are related to an increased risk of transient respiratory destabilisation (risk ratio (RR) 10.2, 95% confidence interval (CI) 1.3 to 78.8, one trial) and vomiting during the procedure (RR 5.4, 95% CI 1.6 to 18.4, one trial). Results are inconclusive for bradycardia with desaturation (RR 1.0, 95% CI 0.2 to 5.0, one trial) and bradycardia without desaturation (RR 3.6, 95% CI 0.7 to 16.9, one trial), due to the limited precision of estimators. However, in mild to moderate bronchiolitis patients, forced expiration combined with conventional techniques produced an immediate relief of disease severity (one trial, 13 participants). AUTHORS' CONCLUSIONS: None of the chest physiotherapy techniques analysed in this review (conventional, slow passive expiratory techniques or forced expiratory techniques) have demonstrated a reduction in the severity of disease. For these reasons, these techniques cannot be used as standard clinical practice for hospitalised patients with severe bronchiolitis. There is high quality evidence that forced expiratory techniques in severe patients do not improve their health status and can lead to severe adverse events. Slow passive expiratory techniques provide an immediate and transient relief in moderate patients without impact on duration. Future studies should test the potential effect of slow passive expiratory techniques in mild to moderate non-hospitalised patients and patients who are respiratory syncytial virus (RSV) positive. Also, they could explore the combination of chest physiotherapy with salbutamol or hypertonic saline.

Oxygen therapy for lower respiratory tract infections in children between 3 months and 15 years of age.

BACKGROUND: Treatment for lower respiratory tract infections (LRTIs) includes administering complementary oxygen. The effectiveness of oxygen therapy and of different delivery methods remains uncertain. OBJECTIVES: To determine the effectiveness and safety of oxygen therapy and oxygen delivery methods in the treatment of LRTIs and to define the indications for oxygen therapy in children with LRTIs. SEARCH METHODS: For this update, we searched CENTRAL, MEDLINE, EMBASE and LILACS from March 2008 to October 2014. SELECTION CRITERIA: Randomised controlled trials (RCTs) or non-RCTs comparing oxygen versus no oxygen therapy or different methods of oxygen delivery in children with LRTI aged from three months to 15 years. To determine the indications for oxygen therapy, we included observational studies or diagnostic test accuracy studies. DATA COLLECTION AND ANALYSIS: Three review authors independently scanned the search results to identify studies for inclusion. Two authors independently performed the methodological assessment and the third author resolved any disagreements. We calculated risk ratios (RRs) and their 95% confidence intervals (CIs) for dichotomous outcomes and adverse events (AEs). We performed fixed-effect meta-analyses for the estimation of pooled effects whenever there was no heterogeneity between included RCTs. We summarised the results reported in the included observational studies for the clinical indicators of hypoxaemia. MAIN RESULTS: In this review update, we included four studies (479 participants) assessing the efficacy of non-invasive delivery methods for the treatment of LRTI in children and 14 observational studies assessing the clinical sign indicators of hypoxaemia in children with LRTIs.Three RCTs (399 participants) compared the effectiveness of nasal prongs or nasal cannula with nasopharyngeal catheter; one non-RCT (80 participants) compared head box, face mask, nasopharyngeal catheter and nasal cannula. The nasopharyngeal catheter was the control group. Treatment failure was defined as number of children failing to achieve adequate arterial oxygen saturation. All included studies had a high risk of bias because of allocation methods and lack of blinded outcome assessment.For nasal prongs versus nasopharyngeal catheter, the pooled effect estimate for RCTs showed a worrying trend towards no difference between the groups (two RCTs; 239 participants; RR 0.93, 95% CI 0.36 to 2.38). Similar results were shown in the one non-RCT (RR 1.0, 95% CI 0.44 to 2.27). The overall quality of this evidence is very low. Nasal obstruction due to severe mucus production was different between treatment groups (three RCTs, 338 participants; RR 0.20, 95% CI 0.09 to 0.44; I(2) statistic = 0%). The quality of this evidence is low.The use of a face mask showed a statistically significant lower risk of failure to achieve arterial oxygen > 60 mmHg than the nasopharyngeal catheter (one non-RCT; 80 participants; odds ratio (OR) 0.20, 95% CI 0.05 to 0.88).The use of a head box showed a non-statistically significant trend towards a reduced risk of treatment failure compared to the nasopharyngeal catheter (one non-RCT; OR 0.40, 95% CI 0.13 to 1.12). The quality of this evidence is very low.To determine the presence of hypoxaemia in children presenting with LRTI, we assessed the sensitivity and specificity of nine clinical signs reported by the included observational studies and used this information to calculate likelihood ratios. The results showed that there is no single clinical sign or symptom that accurately identifies hypoxaemia. AUTHORS' CONCLUSIONS: It appears that oxygen therapy given early in the course of pneumonia via nasal prongs at a flow rate of 1 to 2 L/min does not prevent children with severe pneumonia from developing hypoxaemia. However, the applicability of this evidence is limited as it comes from a small pilot trial.Nasal prongs and nasopharyngeal catheter are similar in effectiveness when used for children with LRTI. Nasal prongs are associated with fewer nasal obstruction problems. The use of a face mask and head box has been poorly studied and it is not superior to a nasopharyngeal catheter in terms of effectiveness or safety in children with LRTI.Studies assessing the effectiveness of oxygen therapy and oxygen delivery methods in children with different baseline risks are needed.There is no single clinical sign or symptom that accurately identifies hypoxaemia in children with LRTI. The summary of results presented here can help clinicians to identify children with more severe conditions.This review is limited by the small number of trials assessing oxygen therapy and oxygen delivery methods as part of LRTI treatment. There is insufficient evidence to determine which non-invasive delivery methods should be used in children with LRTI and low levels of oxygen in their blood.

Chest physiotherapy for acute bronchiolitis in paediatric patients between 0 and 24 months old.

BACKGROUND: This is an update of the original Cochrane review published in 2005 and updated in 2007. Acute bronchiolitis is the leading cause of medical emergencies during winter in children younger than two years of age. Chest physiotherapy is thought to assist infants in the clearance of secretions and to decrease ventilatory effort. OBJECTIVES: The main objective was to determine the efficacy of chest physiotherapy in infants aged less than 24 months old with acute bronchiolitis. A secondary objective was to determine the efficacy of different techniques of chest physiotherapy (for example, vibration and percussion and passive forced exhalation). SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 4) which contains the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to November week 3, 2011), MEDLINE in-process and other non-indexed citations (8 December 2011), EMBASE.com (1990 to December 2011), CINAHL (1982 to December 2011), LILACS (1985 to December 2011) and Web of Science (1985 to December 2011). SELECTION CRITERIA: Randomised controlled trials (RCTs) in which chest physiotherapy was compared against no intervention or against another type of physiotherapy in bronchiolitis patients younger than 24 months of age. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data. Primary outcomes were respiratory parameters and improvement in severity of disease. Secondary outcomes were length of hospital stay, duration of oxygen supplementation and the use of bronchodilators and steroids. No pooling of data was possible. MAIN RESULTS: Nine clinical trials including 891 participants were included comparing physiotherapy with no intervention. Five trials (246 participants) evaluated vibration and percussion techniques and four trials (645 participants) evaluated passive expiratory techniques. We observed no significant differences in the severity of disease (eight trials, 867 participants). Results were negative for both types of physiotherapy. We observed no differences between groups in respiratory parameters (two trials, 118 participants), oxygen requirements (one trial, 50 participants), length of stay (five trials, 222 participants) or severe side effects (two trials, 595 participants). Differences in mild transient adverse effects (vomiting and respiratory instability) have been observed (one trial, 496 participants). AUTHORS' CONCLUSIONS: Since the last publication of this review new good-quality evidence has appeared, strengthening the conclusions of the review. Chest physiotherapy does not improve the severity of the disease, respiratory parameters, or reduce length of hospital stay or oxygen requirements in hospitalised infants with acute bronchiolitis not on mechanical ventilation. Chest physiotherapy modalities (vibration and percussion or forced expiratory techniques) have shown equally negative results.

Oxygen therapy for lower respiratory tract infections in children between 3 months and 15 years of age.

BACKGROUND: Usual practice in lower respiratory tract infections (LRTIs) includes administering complementary oxygen. The effectiveness of oxygen therapy and different methods of delivery is unknown. This review contributes to the rational use of oxygen in the treatment of LRTIs. OBJECTIVES: To determine in the treatment of LRTIs: the effectiveness of oxygen therapy and oxygen delivery methods; the safety of these methods; and indications for oxygen therapy. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2008, issue 2); MEDLINE (January 1966 to March 2008); EMBASE (1990 to December 2007); and LILACS (January 1982 to March 2008). SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing oxygen versus no oxygen therapy or methods of oxygen delivery for hypoxaemic LRTIs in children (3 months to 15 years of age). To determine indications for oxygen therapy, observational studies were included. DATA COLLECTION AND ANALYSIS: We assessed 551 titles. No studies comparing oxygen versus no oxygen were found. Four RCTs comparing delivery methods and 12 observational studies assessing the accuracy of clinical signs indicating hypoxaemia were eligible. A meta-analysis of the RCTs comparing oxygen delivery methods was performed. MAIN RESULTS: Three studies assessed the effectiveness of nasal prongs (NP) versus nasopharyngeal catheters (NPC). The pooled estimate effect showed no differences (OR 0.96; 95% CI 0.48 to 1.93) in treatment failure (number of children failing to achieve adequate SaO2). One study compared the effectiveness of NP versus nasal catheter (NC). No differences were found in treatment failure (the mean number of episodes of desaturation/child: NC group 2.75, SD +/- 2.18 episodes/child; NP group 3, SD +/- 2.5 episodes/child, p = 0.64). Another study compared face mask (FM) and head box (HB) versus NPC. Use of FM showed lower risk of treatment failure (failure to achieve PaO2 > 60 mmHg) than the NPC (OR 0.20; 95% CI 0.55 to 0.88). As did the use of HB compared with NPC (OR 0.40; 95% CI 0.13 to 1.12).Studies assessing the accuracy of signs and/or symptoms indicating hypoxaemia showed that cyanosis, grunting, difficulty in feeding and mental alertness have better specificity in predicting hypoxaemia and its results were consistent among studies. AUTHORS' CONCLUSIONS: NP and NPC seem to be similar in effectiveness and safety when used in patients with LRTI. There is no single clinical sign or symptom that accurately identifies hypoxaemia. Studies identifying the most effective and safe oxygen delivery method are needed.