The priority for this client is to ensure a patent airway by placing him the Fowler's or semi upright seated position. Giving oxygen is warranted but will be given after the client is positioned correctly. ABG's would be helpful in this situation but it not the priority. Auscultation of breath sounds and assessment of mental status are not indicated.

The final stage of a pertussis infection is known as the convalescent phase. This occurs for 2-6 weeks, after the paroxysmal stage of the disease. During this time coughing decreases, and paroxysms are less severe. The infected individual may experience increased susceptibility to upper and lower respiratory conditions for as much as 6 months after resolution of the infection.

Whooping cough, a condition that results in severe paroxysmal coughing fits followed by a long wheezing inspiratory gasp (the "whoop") is caused by the bacteria Bordetella pertussis. Haemophilus influenzae and Klebsiella pneumoniae both commonly cause pneumonia, and RSV is a virus that is frequently implicated in lower respiratory infections of infants and children.

After the catarrhal stage, an individual with pertussis will progress into the paroxysmal stage. It's during this stage that they will experience uncontrollable fits of 5-15 forceful coughs, followed by a "whoop" or gasp as they struggle to inhale. The force of these coughs can be such that they can result in vomiting, epistaxis, subconjunctival hemorrhage, or even broken ribs. 

The incubation period for pertussis, also known as the catarrhal stage, can last as little as 4 days or as long as 42 days, but a typical period is 1-3 weeks. During this stage the disease looks like a regular upper respiratory infection, with sneezing, mild cough, and runny nose. The infected individual is highly infectious at this time, with bacteria spread by airborne droplets after sneezing or cough. 

The correct answer is "Sarcoidosis." Sarcoidosis is the correct answer as this inflammatory condition is frequently found in African-American women in their 40's who present with fatigue and shortness of breath among other symptoms, who also have erythema nodosum on the lower extremities, and have bilateral hilar infiltrates on chest x-ray. This constellation of findings is highly suggestive of sarcoidosis. Sarcoidosis results in the formation of numerous non-necrotizing granulomas, most commonly found in the lungs, that can play a role in the symptoms experienced by these patients. Other findings suggestive of sarcoidosis include elevated serum calcium levels with normal serum PTH levels.

Tuberculosis can present in a similar manner to sarcoidosis, however given the patient's suburban living environment, lack of a travel history, and lack of healthcare exposure, the likelihood of being exposed to tuberculosis is very low, making sarcoidosis a more likely etiology.

While lung cancer can present as shortness of breath with hilar infiltration in chest x-ray, in a relatively young otherwise healthy patient who also has erythema nodosum and in whom the hilar infiltrates are bilateral, sarcoidosis would be a more likely etiology.

The patient does not have any findings consistent with meningitis (leg rash in meningitis is petechial, not erythema nodosum) or pharyngitis.