Afebrile Pneumonia Syndrome Clinical Presentation

Updated: Aug 22, 2023
  • Author: Dagnachew (Dagne) Assefa, MD, FAAP, FCCP; Chief Editor: Girish D Sharma, MD, FCCP, FAAP  more...
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Early symptoms of respiratory disease in neonates and infants are frequently nonspecific and include changes in feeding status, listlessness, irritability, and poor color. Onset may be acute or subacute. Typically, infants are afebrile or have only a low-grade fever (< 102°F).

Viral afebrile pneumonia syndrome (APS) typically has a more rapid onset, with a 1- to 2-day history of rhinorrhea and, often, a brassy cough. Nonspecific findings of poor feeding, lethargy, and irritability may be accompanied by congestion, apnea (uncommon), and cyanosis (rare).

Symptoms of APS from Chlamydia trachomatis typically begin at age 2-19 weeks. Onset is insidious, often occurring over several days to weeks. No signs of systemic illness are apparent, but infants with mild-to-moderate illness often have a repetitive staccato cough (inspiration between each single cough). [1, 10]  In one study, most of the infants with C trachomatis lower respiratory tract infection were afebrile, and 47% had wheezing. [3] A history of conjunctivitis (which may be concurrent) increases the possibility of chlamydial infection. [11]

Ureaplasma urealyticum

U urealyticum is typically associated with prematurity and chronic lung disease. U urealyticum has been routinely isolated from the lower respiratory tract and lung biopsy specimens from infants with low birthweight, premature infants with pneumonia, and infants younger than 3 months who have chronic lung disease. Nevertheless, the role of this organism in development of lower respiratory tract infections in other infants remains unclear. Infection may manifest in this population as chronic lung disease, acute deterioration, or subacute deterioration in lung function.


Clinical manifestations of disease from CMV vary with the age and immunologic status of the child. Although infection following vertical transmission is usually not associated with clinical illness, maternal cervical colonization commonly occurs; therefore, many infants are exposed at birth. Cervical excretion rates are highest among young mothers in lower socioeconomic groups. Most infants infected are asymptomatic, but some may develop interstitial pneumonitis in early infancy. Because CMV infection is common in newborns, its association with afebrile pneumonia has been questioned. Symptoms are typically not distinguishable from those in APS from other causes.

Respiratory syncytial virus

RSV is likely the most common cause of afebrile pneumonia in young infants, although it more frequently causes febrile pneumonia or bronchiolitis, since the incidence of chlamydial APS seems to be decreasing. Peak age of onset is 2-5 months. Infection during the first few weeks of life may produce minimal respiratory signs. Lethargy, irritability, and poor feeding (which signal a possible illness in any young infant) accompanied by periods of apnea may be the major manifestations of infection. Most infants do not require hospitalization. However, the illness can be severe or fatal in some infants, particularly if associated with cyanotic or congenital heart disease, prematurity, or immunodeficiency due to disease or immunosuppressive therapy.

RSV infection is usually epidemic during the winter and early spring months, primarily affects children in the first 3 years of life, and is spread horizontally by household or childcare center contacts. Although wheezing and typical bronchiolitis may be noted, nonspecific symptoms more typical of APS may predominate.


Adenovirus is an infrequent cause of croup and bronchiolitis. In infancy, adenovirus can cause severe pneumonia, which may disseminate, resulting in death. Infants may present with conjunctivitis, pharyngitis, respiratory tract symptoms, and, possibly, gastrointestinal tract disturbances. Less commonly, adenoviral disease may result in more typical APS.

Parainfluenza virus

Parainfluenza virus infections may be epidemic or sporadic. Type 1 occurs every other fall and manifests as croup. Type 2 also occurs in the fall, but disease is typically less severe than that caused by type 1. Type 3 infection occurs in the spring and summer and is usually acquired during the first 2 years of life; it is also a major cause of lower respiratory tract infection. Repeat infection may occur at any age and is usually milder, resulting in upper respiratory tract infections. Individuals with immunodeficiency can develop severe lower respiratory tract infection with prolonged viral shedding. Secondary bacterial infections are common after viral disease. Rarely, apnea may occur in infants younger than 6 months and may necessitate short-term apnea monitoring. Otherwise, APS secondary to infection by parainfluenza virus may be clinically indistinguishable from APS that results from other causes.

Pneumocystis jiroveci

P jiroveci, a pathogen related to fungi, is best known as a cause of opportunistic disease in immunocompromised individuals. Recently, it has also been associated with afebrile pneumonia in immunocompetent infants. Approximately 75% of healthy persons acquire antibody to P jiroveci by age 4 years. Onset of symptoms during the first month of life is rare; peak incidence of infection is from age 2-6 months. The mode of transmission of P jiroveci is unknown. Typically, infection is asymptomatic, but it may cause APS in a small percentage of infants who are exposed to the pathogen.


Physical Examination

Signs of APS are typically nonspecific, and considerable overlap occurs among the various causes. Rarely, infants may display lethargy or irritability and poor color.

Respiratory findings may include cough, tachypnea, and crackles. Cough, which may be staccato (particularly in C trachomatis infection), is nearly universal. Tachypnea and crackles are usually present. In APS caused by C trachomatis, auscultatory findings may be out of proportion to the overall healthy appearance of the infant.

Respiratory distress is typically only mild to moderate and may include the following:

  • Retractions

  • Grunting

  • Flaring

Apnea is uncommon. Cyanosis is rare.

Other pulmonary findings are possible but uncommon and may include the following:

  • Decreased aeration

  • Dullness to percussion

  • Wheezing [12]

Conjunctivitis suggests C trachomatis infection (present concurrently or in the history in half of cases). GI tract, conjunctival, or pharyngeal involvement may suggest adenovirus infection. Concomitant hepatosplenomegaly or lymphadenopathy may suggest CMV infection.