Not every cough in bronchiolitis season is bronchiolitis
- Penelope Ann Bryant,
- Published 28 August 2009
A 2-month-old male infant presented to hospital for the third time in late autumn with a 4 week history of cough and respiratory distress. He had presented to hospital on two occasions during the previous two weeks, and had twice been discharged with a diagnosis of bronchiolitis, based on clinical findings and the season. That the nasopharyngeal aspirate (NPA) was negative for respiratory viruses did not alter the diagnosis as this was felt to be a common false negative finding. However his cough worsened and on his third presentation he had respiratory distress with bilateral crackles and wheeze. The C reactive protein was 121 mg/l but the NPA was again negative for viruses. He was investigated for atypical causes of lower respiratory tract infection and the NPA was positive for Chlamydia trachomatis by polymerase chain reaction. He was treated with a 5 day course of azithromycin and made a full recovery.
Among the most common causes of infants and young children presenting to health professionals over the autumn and winter months are lower respiratory tract infections. The vast majority of these will be ascribed a viral aetiology, especially in the age group under 1 year and when prevailing respiratory viruses cause a high incidence of bronchiolitis. This is true, as this case shows, even in the face of negative results and when the clinical course is not typical. This case highlights the need to consider other causes of lower respiratory tract symptoms in the peak season for bronchiolitis.
An 8-week-old male infant presented in November to hospital for the third time with a 4 week history of cough, intermittent respiratory distress and nasal congestion. He had initially presented to his local hospital at 6 weeks of age with a cough and had been discharged from the accident and emergency department with an ipratropium bromide inhaler for presumed bronchiolitis. The nasopharyngeal aspirate (NPA) result was subsequently negative for respiratory syncitial virus (RSV), influenza A and B, parainfluenza and adenovirus. He was admitted to our hospital 9 days later with worsening cough and vomiting. His blood results were unremarkable with a white blood cell count of 11.3×109/l and C reactive protein (CRP) of 4 mg/l. Chest radiography showed no focal consolidation but possible peribronchial thickening (fig 1). He was discharged the following day with a clinical diagnosis of likely bronchiolitis.
He presented to the paediatric infectious diseases ward 5 days later with worsening symptoms including respiratory distress, although he was still feeding well. He had been born at term following an uneventful pregnancy during which his mother had been well. He had been completely healthy until 1 month of age when the current symptoms had started. Clinically, the patient was afebrile and he did not have an oxygen requirement. He had nasal congestion and mild respiratory distress with bilateral crackles and wheeze on auscultation.
Investigations were as follows: haemoglobin 9.9 g/dl, white blood cell count 19.1×109/l, neutrophils 11.2×109/l, lymphocytes 5.0×109/l, platelets 701×109/l, and CRP 121 mg/l. Biochemistry including liver function tests were normal. A chest radiograph was unchanged from previously.
An NPA at admission was again negative for the above viruses and additionally metapneumovirus. The progression of symptoms in addition to abnormal blood results and negative NPA results prompted investigation for atypical causes of lower respiratory tract infection. The NPA was positive for Chlamydia trachomatis by polymerase chain reaction (PCR).
The infant was treated with a 5 day course of azithromycin 10 mg/kg after which his symptoms completely resolved.
OUTCOME AND FOLLOW-UP
Further history revealed that his mother had had no vaginal discharge during pregnancy. His parents were both investigated for carriage of C trachomatis and were both treated.
Six weeks after treatment had finished, the infant once again presented to hospital with cough and respiratory distress. Ironically on this occasion his NPA was positive for RSV. He recovered fully over the course of a few days with no further problems.
Acute lower respiratory tract infections are one of the most common reasons for infants and young children to attend primary and secondary medical care in the autumn and winter months. In recent studies of the aetiology of community acquired pneumonia in paediatric inpatients, the most frequent cause is viral.1,2 Of these, 50–60% are due to RSV. This proportion is higher when only infants under the age of 12 months are included, and during the season of peak incidence of bronchiolitis when the proportion may be over 90% in this population.3 Bronchiolitis season in the UK begins in mid autumn and continues through winter. In 2008, the peak of laboratory reports of RSV was in week 48, corresponding to the last week in November.3
Early in the season it is not uncommon for infants with a clinical picture of bronchiolitis to have no virus identified. Studies comparing techniques of identifying RSV in samples in bronchiolitis have found that the most commonly used method of immunofluorescence is less sensitive (69–93%) than PCR (97–100%).4,5 RSV negative bronchiolitis is therefore a diagnosis that is commonly accepted.
However, bacterial pathogens should also be considered as these represent 7–20% of lower respiratory tract infections.1,2 Specifically, Chlamydia species (C trachomatis, C pneumonia and C psittaci) account for 1–3% of community acquired pneumonia in resource-rich countries.1,2,6,7 In a UK study of patients admitted to hospital with bronchiolitis not attributable to RSV, 17.1% were identified by nested PCR as being positive for C trachomatis.6 In addition, the ongoing need for awareness of emerging pathogens is highlighted by the recent identification of causative agents of bronchiolitis such as Parachlamydia acanthamoebae.8
C trachomatis is a small intracellular organism which is difficult to culture. It is most commonly associated with sexually transmitted diseases and ophthalmia neonatorum (conjunctivitis in the newborn). In adult females it can cause pelvic inflammatory disease leading to infertility and ectopic pregnancies. However, infection is asymptomatic in 70% of females and 50% of males, so it is easy to be unaware of transmission.9
The incidence of genitourinary chlamydial infection has been rising steadily since the mid 1990s. It increased by 5% between 2004 and 2005.9 Rates are highest in the under 25-year-olds with greater than 1% of 16–19-year-old females and 20–24-year-old males diagnosed with C trachomatis infection in the UK.9 Left untreated pregnant women can pass the infection to the baby around the time of delivery. Babies born to women with C trachomatis have a 40–50% chance of developing conjunctivitis and a 10% chance of developing pneumonia.10
C trachomatis pneumonia may be difficult to distinguish from infection caused by RSV under the age of 3 months as they both present with cough and tachypnoea and auscultation usually reveals crackles. Slow onset of symptoms and lack of fever are described as distinguishing features of C trachomatis pneumonia, although infants in this age group with RSV are less likely to have fever than older children.
A recent study from Taiwan of the epidemiology and presentation of C trachomatis pneumonia in infants younger than 6 months found that 83% presented with tachypnoea and 72% were afebrile at presentation.11 The median age of presentation was 2.5 months and ranged from 1 day to 6 months. There was a preceding prodrome of rhinorrhoea in 67%, but only 22% had the characteristic staccato cough. These clinical findings are replicated in other case reports12 and case series.10 In the cases from Taiwan, the only consistent laboratory investigation between chlamydia positive and negative pneumonia was eosinophilia (p=0.046).
Chest radiography in C trachomatis pneumonia usually shows hyperinflation with diffuse bilateral changes similar to findings with RSV infection.8 Rapid diagnosis of chlamydial infection can be made with PCR of NPA samples. In diagnosing the infant the parents also need investigation and treatment.
Even in peak bronchiolitis season, insidious onset of symptoms in a young infant that do not improve should alert the physician to this alternate diagnosis. Co-infection with C trachomatis and RSV has been reported,9 so it is important to consider this diagnosis in the right clinical setting even if the investigations for RSV are positive.
In the peak season for bronchiolitis other causes of lower respiratory infection should be considered early if the clinical course is not typical, especially if results are not supportive.
Consider other causes of lower respiratory tract infection when the response to treatment is not as expected.
Rapid diagnosis of chlamydial infection by PCR is widely available.
In a baby diagnosed with chlamydial infection, both parents must be screened.
Competing interests: none.
Patient consent: Patient/guardian consent was obtained for publication