Common cold

Abstract

Introduction

Each year, children suffer up to 5 colds and adults have two to three infections, leading to time off school or work, and considerable discomfort. Most symptoms resolve within 1 week, but coughs often persist for longer.

Methods and outcomes

We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments for common cold? We searched: Medline, Embase, The Cochrane Library, and other important databases up to January 2010 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

Results

We found 21 systematic reviews and RCTs that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

Conclusions

In this systematic review we present information relating to the effectiveness and safety of the following interventions: analgesics or anti-inflammatory drugs, antibiotics, antihistamines, decongestants for short-term and for long-term relief, decongestants plus antihistamines, echinacea, steam inhalation, vitamin C, and zinc (intranasal gel or lozenges).

Key Points

Transmission of common cold infections is mostly through hand-to-hand contact rather than droplet spread. Several types of virus can cause symptoms of colds.

• Each year, children suffer up to 5 colds and adults have two to three infections, leading to time off school or work and considerable discomfort. Most symptoms resolve within 1 week, but coughs often persist for longer.

Nasal and oral decongestants reduce nasal congestion over 3 to 10 hours, but we don't know how effective decongestants are for longer-term relief (>10 hours).

Antibiotics don't reduce symptoms overall, and can cause adverse effects and increase antibiotic resistance.

• Antibiotics may improve symptoms after 5 days compared with placebo in people with nasopharyngeal culture-positive Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae, but it is difficult to identify which people may have these infections.

Vitamin C seems unlikely to reduce the duration or severity of cold symptoms compared with placebo.

• We don't know whether zinc gel or lozenges, echinacea, steam inhalation, or analgesics or anti-inflammatory drugs reduce the duration of symptoms of colds.

Antihistamines may slightly reduce runny nose and sneezing, but their overall effect seems small. Some antihistamines may cause sedation or arrhythmias.

We found insufficient evidence to assess whether decongestants plus antihistamines are effective in reducing cold symptoms.

About this condition

Definition

Common colds are defined as upper respiratory tract infections that affect the predominantly nasal part of the respiratory mucosa. Because upper respiratory tract infections can affect any part of the mucosa, it is often arbitrary whether an upper respiratory tract infection is called a "cold" or "sore throat" ("pharyngitis" or "tonsillitis"), "sinusitis", "acute otitis media", or "bronchitis" (see figure 1 in review on sore throat). Sometimes all areas (simultaneously or at different times) are affected during one illness. Symptoms include sneezing, rhinorrhoea (runny nose), headache, and general malaise. In addition to nasal symptoms, half of sufferers experience sore throat, and 40% experience cough. This review does not include treatments for people with acute sinusitis (see review on acute sinusitis), acute bronchitis (see review on acute bronchitis), or sore throat (see review on sore throat). One prospective US study (1246 children enrolled at birth) found that children who had frequent colds when aged 2 or 3 years were twice as likely to experience frequent colds at year 6 compared with children who had infrequent colds at 2 or 3 years (RR 2.8, 95% CI 2.1 to 3.9).

Incidence/ Prevalence

Upper respiratory tract infections, nasal congestion, throat complaints, and cough are responsible for 11% of general practice consultations in Australia. Each year, children suffer about 5 such infections and adults two to three infections. One cross-sectional study in Norwegian children aged 4 to 5 years found that 48% experienced more than two common colds annually.

Aetiology/ Risk factors

Transmission of common cold infection is mostly through hand-to-hand contact, with subsequent passage to the nostrils or eyes — rather than, as commonly perceived, through droplets in the air. Common cold infections are mainly caused by viruses (typically rhinovirus, but also coronavirus and respiratory syncytial virus, or metapneumovirus and others). For many colds, no infecting organism can be identified.

Prognosis

Common colds are usually short lived, lasting a few days, with a few lingering symptoms lasting longer, especially cough. Symptoms peak within 1 to 3 days and generally clear by 1 week, although cough often persists. Although they cause no mortality or serious morbidity, common colds are responsible for considerable discomfort, lost work, and medical costs.

Aims of intervention

To relieve symptoms, shorten the illness, or reduce complications; to reduce infectivity to others, with minimal adverse effects from treatments.

Outcomes

Symptom severity: includes cure rate, time away from work or school, and symptom duration; occurrence of complications; adverse effects of treatment.

Methods

Clinical Evidence search and appraisal January 2010. The following databases were used to identify studies for this systematic review: Medline 1966 to January 2010, Embase 1980 to January 2010, and The Cochrane Database of Systematic Reviews 2009, Issue 4 (1966 to date of issue). An additional search within The Cochrane Library was carried out for the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA). We also searched for retractions of studies included in the review. Abstracts of the studies retrieved from the initial search were assessed by an information specialist. Selected studies were then sent to the contributor for additional assessment, using predetermined criteria to identify relevant studies. Study design criteria for inclusion in this review were: published systematic reviews of RCTs and RCTs in any language, at least single blinded, and containing >20 individuals of whom >80% were followed up. We required 7 days of follow-up to include studies; however, we report outcomes within the studies at shorter timeframes than these. We excluded all studies described as "open", "open label", or not blinded unless blinding was impossible. We included systematic reviews of RCTs and RCTs where harms of an included intervention were studied applying the same study design criteria for inclusion as we did for benefits. In addition we use a regular surveillance protocol to capture harms alerts from organisations such as the US FDA and the UK MHRA, which are added to the reviews as required. Where possible, we have excluded RCTs undertaken solely in people with experimentally induced colds, although meta-analyses in some systematic reviews do include such RCTs. We have also excluded RCTs that only assessed the outcome of bacteriological clearance. We performed a broad search for RCTs of any decongestant, analgesic, or anti-inflammatory in people with common cold, and included any RCTs of sufficient quality. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).

Table.

GRADE Evaluation of interventions for Common cold.

Important outcomes	Complications, Symptom severity
Studies (Participants)	Outcome	Comparison	Type of evidence	Quality	Consistency	Directness	Effect size	GRADE	Comment
What are the effects of treatments for common cold?
at least 10 (at least 3592)	Symptom severity	Antihistamines versus placebo	4	–1	0	–2	0	Very low	Quality point deducted for incomplete reporting of results. Directness points deducted for inclusion of experimentally induced colds and for unclear clinical importance of results
7 (703)	Symptom severity	Decongestants for short-term relief versus placebo	4	–1	0	–1	0	Low	Quality point deducted for incomplete reporting of results. Directness point deducted for unclear clinical importance of results
at least 3 (at least 659)	Symptom severity	Decongestants for long-term relief versus placebo	4	–2	0	0	0	Low	Quality points deducted for incomplete reporting of results and weak methods (randomisation not reported)
3 (461)	Symptom severity	Decongestants plus antihistamines versus placebo	4	–1	0	–1	0	Low	Quality point deducted for incomplete reporting of results. Directness point deducted for unclear clinical importance of results
2 (254)	Symptom severity	Analgesics or anti-inflammatory drugs versus placebo	4	–1	0	–1	0	Low	Quality point deducted for weak methods in 1 RCT. Directness point deducted for small number of analgesics assessed
at least 10 (at least 1630)	Symptom severity	Echinacea versus placebo	4	–1	0	–2	0	Very low	Quality point deducted for incomplete recording of results. Directness points deducted for clinical heterogeneity between RCTs (including statistical heterogeneity in 1 analysis), significance of results depending on the analysis undertaken, and for the use of additional supplements in some RCTs
2 (146)	Symptom severity	Steam inhalation versus sham inhalation	4	−3	0	0	0	Very low	Quality points deducted for sparse data, uncertainty about the validity of control, and unclear symptom score indices
10 (at least 1212)	Symptom severity	Zinc lozenges versus placebo	4	–1	–1	0	0	Low	Quality point deducted for inclusion of people with experimentally induced colds. Consistency point deducted for heterogeneity between RCTs
3 (451)	Symptom severity	Intranasal zinc gel versus placebo	4	0	0	–2	0	Low	Directness points deducted for wide range of doses used in RCTs, inclusions of slightly different population, and varying significance of results depending on analysis undertaken
at least 7 (at least 3294 cold episodes)	Symptom severity	Vitamin C versus placebo	4	–1	0	–1	0	Low	Quality point deducted for analysis by cold episodes not people. Directness point deducted for wide range of treatment protocols in RCTs
at least 6 (at least 1482)	Symptom severity	Antibiotics versus placebo	4	–1	0	–1	0	Low	Quality point deducted for incomplete reporting of results (and unclear in 1 review). Directness point deducted for inclusion of people with additional bacterial infection

We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.

Glossary

Low-quality evidence

Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.

Very low-quality evidence

Any estimate of effect is very uncertain.

Acute sinusitis

Acute bronchitis

Sore throat

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