Common cold

Abstract

Introduction

Each year, children suffer up to 5 colds and adults have 2-3 infections, leading to time off school or work, and considerable discomfort. Most symptoms resolve within a 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 May 2007 (BMJ 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 19 systematic reviews, RCTs, or observational studies 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 (norephedrine, oxymetazoline, or pseudoephedrine), decongestants plus antihistamine, 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 five colds and adults have two to three infections, leading to time off school or work and considerable discomfort. Most symptoms resolve within a week, but coughs often persist for longer.

Nasal and oral decongestants reduce nasal congestion over 3-10 hours, but we don't know whether they are effective in the longer term (more than 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, 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 don't know whether decongestants plus antihistamines reduce cold symptoms or cold duration.

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 five such infections and adults two to three infections. One cross-sectional study in Norwegian children aged 4-5 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 1-3 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

Cure rate; duration of symptoms; time away from work or school; incidence of complications; adverse effects of treatment.

Methods

BMJ Clinical Evidence search and appraisal May 2007. The following databases were used to identify studies for this systematic review: Medline 1966 to May 2007, Embase 1980 to May 2007, and The Cochrane Database of Systematic Reviews and Cochrane Central Register of Controlled Clinical Trials 2007, Issue 2. Additional searches were carried out using these websites: NHS Centre for Reviews and Dissemination (CRD) — for Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA), Turning Research into Practice (TRIP), and NICE. 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 author for additional assessment, using pre-determined criteria to identify relevant studies. Study design criteria for inclusion in this review were: published systematic reviews and RCTs in any language, at least single blinded, and containing more than 20 individuals of whom more than 80% were followed up. The minimum length of follow-up required to include studies was 7 days. We excluded all studies described as "open", "open label", or not blinded for subjective outcomes (unwell) but did not for objective outcomes (fever). We use a regular surveillance protocol to capture harms alerts from organisations such as the FDA and the UK Medicines and Healthcare products Regulatory Agency (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. We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table ).

Table.

GRADE evaluation of interventions for common cold

Important outcomes	Cure rates, symptom severity, time away from work/school, adverse effects
Number of studies (participants)	Outcome	Comparison	Type of evidence	Quality	Consistency	Directness	Effect size	GRADE	Comment
What are the effects of treatments?
15 (5286)	Symptom relief	Antihistamines v placebo	4	−1	0	−2	0	Very low	Quality point deducted for incomplete reporting of results. Directness points deducted for inclusion of RCTs of experimentally induced colds and for inclusion of other interventions
12 (1249)	Symptom relief	Decongestants (short-term relief) v placebo	4	−1	0	0	0	Moderate	Quality point deducted for subjective assessment of outcome
2 (432)	Symptom relief	Decongestants (long-term relief) v placebo	4	−2	0	0	0	Low	Quality points deducted for uncertainly about method of randomisation and subjective assessment of outcome
2 (302)	Symptom duration	Echinacea v placebo	4	0	−1	0	0	Moderate	Consistency point deducted for conflicting results
3 (230)	Symptom relief	Steam inhalation v sham inhalation	4	−2	−1	−1	0	Very low	Quality points deducted for poor methodologies and reporting of results, and uncertainty about validity of control. Consistency point deducted for conflicting results. Directness point deducted for inclusion of RCTs of experimentally induced colds
13 (at least 516 people)	Symptom duration	Zinc lozenges v placebo	4	−1	−1	−2	0	Very low	Quality point deducted for incomplete reporting of results. Consistency point deducted for conflicting results. Directness points deducted for comparing different formulations and in people infected with different viruses
3 (453)	Symptom duration	Zinc intranasal gel v placebo	4	0	0	0	0	High
4 (2753)	Symptom relief	Vitamin C v placebo	4	0	0	0	0	High
7 (3294 cold episodes)	Symptom duration	Vitamin C v placebo	4	0	0	0	0	High
2 (2179)	Cure rates	Antibiotics v placebo	4	0	−1	0	0	Moderate	Consistency point deducted for different results on sub analysis

Type of evidence: 4 = RCT; 2 = Observational; 1 = Non-analytical/expert opinion Consistency: similarity of results across studies Directness: generalisability of population or outcomes Effect size: based on relative risk or odds ratio

Glossary

High-quality evidence

Further research is very unlikely to change our confidence in the estimate of effect

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.

Moderate-quality evidence

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

Very low-quality evidence

Any estimate of effect is very uncertain.

Acute sinusitis

Acute bronchitis

Sore throat

Disclaimer

The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients.To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.