Differentials
Hay fever (allergic rhinitis)
SIGNS / SYMPTOMS
Rhinitis occurs in response to exposure to specific allergens.
Chronic fluctuating course, according to allergen exposure and seasonal pattern.
The presence of sore throat would make a common cold more likely.
Other features of atopy suggestive of condition.
INVESTIGATIONS
Allergen skin patch testing and in vitro specific IgE determination are diagnostic tests.
Chronic sinusitis
SIGNS / SYMPTOMS
Symptoms longer than 6 weeks. Usually diagnosed with the aid of radiological studies. Common clinical characteristics of chronic sinusitis include hyposmia or anosmia.
More commonly characterised by chronic inflammation than a bacterial infection, especially in adults.
INVESTIGATIONS
Sinus CT scans are abnormal in sufferers of chronic sinusitis.
Tonsillitis
SIGNS / SYMPTOMS
Usually in children and adolescents aged <15 years. May have a history of contact with an infected person, particularly in enclosed spaces.
Tonsillar swelling or exudates and tender anterior cervical glands.
Most patients with acute streptococcal tonsillitis have a high temperature and absence of cough.
Use of the McIsaac score can help to discriminate the likelihood of an acute sore throat being from group A streptococcus (GAS); a score of 2 or 3 should lead to obtaining a throat swab. [ Sore Throat (Pharyngitis) Evaluation and Treatment Criteria (McIsaac) Opens in new window ] [27]
INVESTIGATIONS
A positive throat culture confirms the diagnosis in most cases.
Rapid streptococcal antigen tests can be used for immediate point-of-care testing.
Acute pharyngitis
SIGNS / SYMPTOMS
GAS pharyngitis occurs most commonly in children and adolescents aged <15 years. Close contact with a person with a GAS presentation may be noted in the history.
Absence of cough, or presence of cervical adenopathy or pharyngeal exudate in GAS pharyngitis.
Use of the McIsaac score [ Sore Throat (Pharyngitis) Evaluation and Treatment Criteria (McIsaac) Opens in new window ] can help to discriminate the likelihood of an acute sore throat being from group A streptococcus (GAS); a score of 2 or 3 should lead to obtaining a throat swab.[27]
INVESTIGATIONS
A positive throat culture confirms the diagnosis in most cases.
Rapid streptococcal antigen tests can be used for immediate point-of-care testing.
Scarlet fever
SIGNS / SYMPTOMS
History of GAS pharyngitis.
Close contact with a person with scarlet fever or other GAS presentation.
Children aged 1 to 10 years. Uncommon in children aged <1 year and adults.
Presence of characteristic scarlatiniform rash. Strawberry tongue may be seen.
Absence of cough or other viral symptoms (e.g., rhinorrhoea).
INVESTIGATIONS
Diagnosis is usually clinical.
Rapid antigen detection tests may be used if available, and will be positive for GAS if GAS infection is present.
Bacterial culture or PCR may be used when rapid tests are not routinely used or recommended, and will be positive for GAS if GAS infection is present.
Acute sinusitis
SIGNS / SYMPTOMS
Acute disease often due to an infectious cause.
Usually clinically diagnosed and may present with nasal congestion, cough, discoloured nasal mucous, and facial pressure/pain.
Facial tenderness is a rare and unreliable sign; however, reproducible pain on percussion of frontal and maxillary sinuses strongly indicates acute bacterial sinusitis. Dental pain and failure of a topical or oral decongestant increases the likelihood of acute bacterial sinusitis.
INVESTIGATIONS
Diagnosis is clinical.
Infectious mononucleosis
SIGNS / SYMPTOMS
Often sub-clinical in young children.
Well-described syndrome with maculopapular rash, fatigability, fever, laryngitis, and malaise.
Hepatosplenomegaly common.
INVESTIGATIONS
Lymphocytosis on FBC.
Positive heterophile antibody test usually diagnostic; may be false-negative in early stages of the illness.
EBV antibody titres can help differentiate acute and chronic forms of EBV infection.
Seasonal influenza
SIGNS / SYMPTOMS
Fever, headache, muscle aches, and malaise are predominant features.
Symptoms more severe than common cold.
Fever greater than 38°C (>100.4°F) suggestive in adults.
May lead to prolonged period of absenteeism/inactivity.
Can lead to severe complications in older and immunocompromised people.
INVESTIGATIONS
Viral culture, direct immunofluorescent-antibody staining, and reverse transcriptase-polymerase chain reaction are recognised tests.
Coronavirus disease 2019 (COVID-19)
SIGNS / SYMPTOMS
May give history of unwell contacts. Consider the current epidemiological situation.
Signs and symptoms are similar so it may be difficult to differentiate between the conditions clinically.
Fever is less common in people with the common cold compared to those with COVID-19, and headache, rhinorrhoea, myalgia, and sore throat are more common in people with the common cold compared to those with COVID-19. A greater number of general symptoms may lead to a diagnosis of common cold rather than COVID-19.[31]
INVESTIGATIONS
Real-time reverse transcription polymerase chain reaction (RT-PCR) is positive for SARS-CoV-2 RNA. Rapid antigen tests may also be used.
Avian influenza A (H5N1) virus infection
SIGNS / SYMPTOMS
Clinical features typical of influenza (e.g., fever, cough, sore throat, muscle aches, malaise), usually in a community where H5N1 virus is circulating or in someone who has travelled to such a community.
INVESTIGATIONS
Viral culture, direct immunofluorescent-antibody staining, and reverse transcriptase-PCR will detect influenza virus. The most definitive means of identifying H5N1 influenza A virus is specific real-time reverse transcriptase-PCR testing that can be performed at specialist laboratories. It can be done directly on patient specimens (e.g., nasopharyngeal swab or aspirate, nasal wash and swab, or tracheal aspirate) or on cultured virus from patient specimens.
Avian influenza A (H7N9) virus infection
SIGNS / SYMPTOMS
Clinical features typical of influenza (e.g., fever, cough, sore throat, muscle aches, malaise), usually in a community where H7N9 virus is circulating or in someone who has travelled to such a community.
INVESTIGATIONS
The test of choice for the diagnosis of H7N9 infection is reverse transcriptase-PCR testing for Asian lineage A (H7N9) virus RNA. The test can be performed at specialist laboratories. An upper respiratory tract specimen (e.g., nasal swab, throat swab, nasopharyngeal swab or aspirate) can be used, but a lower respiratory tract sample (e.g., sputum, tracheal aspirate, bronchoalveolar lavage) is less likely to give a false-negative result.
Pertussis
SIGNS / SYMPTOMS
Initial upper respiratory symptoms may give way several weeks later to an increased severity of cough, with paroxysmal coughing first increasing in frequency, then remaining constant for several weeks. There may be inspiratory whooping and post-tussive vomiting. Inspiratory stridor may be heard on auscultation.
INVESTIGATIONS
Evidence of Bordetella pertussis from nasopharyngeal swabs or aspirates.
Respiratory syncytical virus infection
SIGNS / SYMPTOMS
History of exposure to RSV.
Mainly affects infants aged <6 months and those with a history of prematurity or certain comorbidities.
Seasonal outbreaks during winter (may vary between regions).
Increased work of breathing, wheeze, apnoea, or poor feeding may be noted in infants.
INVESTIGATIONS
PCR is positive for RSV RNA.
Diphtheria
SIGNS / SYMPTOMS
May be a history of exposure or travel to endemic area.
Sore throat and low-grade fever (usually <39°C [<102°F]) followed by dysphagia, dysphonia, dyspnoea, and a croupy cough if there is extension of the pseudomembrane and/or involvement of the posterior pharyngeal and laryngeal nerves.
Grey-brown pseudomembrane may form over the tonsils and/or pharynx after 2 to 5 days of sore throat. Without treatment, it can thicken and spread. Neck swelling and lymphadenopathy may cause characteristic bull-neck appearance.
INVESTIGATIONS
Microscopy and cultures from nose and throat swabs, taken when possible from beneath the pseudomembrane, positive for Corynebacterium diphtheriae.
Meningococcal disease
SIGNS / SYMPTOMS
May present with non-specific respiratory signs/symptoms. May present with triad of tachycardia, low blood pressure, and high fever.
As the illness develops, thirst, respiratory distress, a petechial rash, peripheral vasoconstriction, altered consciousness, photophobia, hypotonia, neck stiffness, seizures, and tachycardia may be present.
In infants, a bulging fontanelle and a characteristic high-pitched cry may occur.
A positive Kernig's or Brudzinski's sign indicates meningeal inflammation and is suggestive of meningitis; is present only in a minority of patients.
INVESTIGATIONS
Isolation of Neisseria meningitidis from a sterile body site (blood, CSF, joint, pleural fluid, pericardial fluid, or aspiration or biopsy of a purpuric lesion) is the definitive test for diagnosis of invasive meningococcal infections.
HIV seroconversion illness
SIGNS / SYMPTOMS
Many HIV-infected individuals develop an acute clinical illness that typically occurs 2 to 4 weeks after exposure to HIV.
Often recognised in retrospect since features are non-specific.
Onset is acute and lasts up to 2 weeks.
Common symptoms are a glandular fever-type illness with fever, malaise, myalgia, pharyngitis, headaches, diarrhoea, neuralgia or neuropathy, lymphadenopathy, maculopapular rash, and mucocutaneous ulceration.
INVESTIGATIONS
Humoral immunodeficiency shows low immunoglobulin levels. Cellular immunodeficiency indicates T-cell dysfunction and/or HIV.
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