A series by Basi et al [30] that included 2,706 patients hospitalized with community-acquired PNA similarly showed that about one- third had radiographs initially interpreted as negative for PNA, with minimal change in this interpretation on retrospective review of a random subgroup. These two studies call into question the usefulness of radiographs in patients with a high pretest probability of PNA. That being said, data from many of the studies that suggested the low utility of chest radiographs in Variant 1 also demonstrate a relatively high incidence of PNA on chest radiographs in patients with physical examination findings, abnormal vital signs, leukocytosis, or other risk factors, such as advanced age [21-25]. For example, Benacerraf et al [21] reported that a subgroup of patients <40 years of age with an abnormal physical examination were about six times more likely to have an acute finding on their chest radiograph. Speets et al [31] evaluated 192 patients with a clinical suspicion of PNA by general practitioners and found that the post- test probability of PNA was changed by chest radiographic results in 53% of patients, with a 47% decrease in probability and a 6% increase in probability. Patient management changed following a chest radiograph in 69% of patients. These data would seem to support the routine use of chest radiographs to confirm the diagnosis of PNA in this clinical variant. Current IDSA/ATS guidelines also support this approach [4]. In a population of ED patients who received a chest radiograph for respiratory complaints, Heckerling [22] found that over 75% of the patients with dementia had PNA on their chest radiograph regardless of physical examination findings. The authors postulate that aspiration related to altered level of consciousness and compromised epiglottic closure could account for the high prevalence of PNA amongst these patients.
Acute Respiratory Illness in Immunocompetent Patients. A series by Basi et al [30] that included 2,706 patients hospitalized with community-acquired PNA similarly showed that about one- third had radiographs initially interpreted as negative for PNA, with minimal change in this interpretation on retrospective review of a random subgroup. These two studies call into question the usefulness of radiographs in patients with a high pretest probability of PNA. That being said, data from many of the studies that suggested the low utility of chest radiographs in Variant 1 also demonstrate a relatively high incidence of PNA on chest radiographs in patients with physical examination findings, abnormal vital signs, leukocytosis, or other risk factors, such as advanced age [21-25]. For example, Benacerraf et al [21] reported that a subgroup of patients <40 years of age with an abnormal physical examination were about six times more likely to have an acute finding on their chest radiograph. Speets et al [31] evaluated 192 patients with a clinical suspicion of PNA by general practitioners and found that the post- test probability of PNA was changed by chest radiographic results in 53% of patients, with a 47% decrease in probability and a 6% increase in probability. Patient management changed following a chest radiograph in 69% of patients. These data would seem to support the routine use of chest radiographs to confirm the diagnosis of PNA in this clinical variant. Current IDSA/ATS guidelines also support this approach [4]. In a population of ED patients who received a chest radiograph for respiratory complaints, Heckerling [22] found that over 75% of the patients with dementia had PNA on their chest radiograph regardless of physical examination findings. The authors postulate that aspiration related to altered level of consciousness and compromised epiglottic closure could account for the high prevalence of PNA amongst these patients.