Consideration of A Nosocomial Outbreak of Influenza A

influenza seasonThe first reported outbreak of influenza A during 1974 occurred in the third week of February at the University of Illinois in Urbana. Within two weeks, outbreaks were reported on the east coast. During the 1973-1974 influenza season, the mortality due to pneumonia and influenza for all 121 reporting cities in the United States did not rise significandy above the endemic level, except during the weeks of March 1 through April 30. The late onset of the outbreak almost certainly accounted for the delay in considering the diagnosis in the present series. This small epidemic was six days old, and all nosocomial cases had become symptomatic before the correct diagnosis was even considered. The present nosocomial outbreak lasted only seven days, and thereafter, no new cases of influenza-like illness were seen in the hospital.

Since no serologic studies were made of other patients hospitalized during that period of time, the actual prevalence of infection could not be established. There is no reason to believe that the precautions of isolation imposed played any role in curtailing the epidemic. Indeed, it is surprising that no more symptomatic cases appeared, in view of the number of persons exposed who suffered from severe underlying disease.

Another feature of the present outbreak was the severity of the disease in the compromised hosts, none of whom had received influenza vaccine. This had been reported earlier in several studies. It is intriguing that each of the recognized patients developed pneumonia. A search of the four medical wards showed no other patients with unexplained fever. Thus, the rate of pulmonary complication seems extraordinarily high. The severity of the disease is further attested to by the fact that six of the nine patients died, either due to the disease itself or the complications it produced.

Focal bacterial pneumonia is a common complication of viral influenza. Even though all of our patients developed pneumonic complications, none of them developed a secondary bacterial infection of the lungs. This was unexpected, since isolated viral pneumonia is the least frequent of the serious complications, secondary bacterial pneumonia being observed far more often.

Influenza causes an acute, prostrating, but relatively benign illness. The previously healthy adults who develop serious or life-threatening pulmonary complications almost always have either secondary bacterial pneumonia or combined influenza and bacterial (usually pneumococcal or staphylococcal) pulmonary infection. Case 9 shows that this may not always be so and that primary influenzal pneumonia may cause overwhelming pulmonary disease in a robust, previously healthy individual. Through the intercity infectious disease group (a New York-New Jersey group), we have become aware of a small number of similar cases occurring both in the 1975 and 1976 influenza epidemic periods. Equally surprising in our patient (case 9) was the severe pleuritic pain, which occurred early in the course of his illness. bacterial infectionThis is not a part of the syndrome of influenza viral pneumonia. It is possible that the patient’s pleurisy resulted from the pulmonary infarcts found at autopsy; however, this seems unlikely. There was no roentgenologic evidence of pulmonary infarction on admission, and the emboli almost certainly supervened as a consequence of the use of intravenous catheters during hospitalization. There was never any evidence of bacterial pneumonia to account for the pain. Two other negative findings were also somewhat unexpected in view of the serologic evidence of influenza. First, the autopsy showed hemorrhagic pneumonia and pulmonary infarction, but there were no hyaline alveolar membranes.Secondly, no influenza virus was recovered from the lung. This may have related to the fact that the patient was improving and died not of the viral pneumonia but of the pulmonary emboli.

It is interesting that the first case recognized was seen in the medical intensive care unit. It is entirely possible that the intrahospital epidemic might have been overlooked had not an attending physician suggested that the ward from which she had been transferred be searched for viral infection.

The source of the hospital epidemic could not be identified, but this is hardly surprising. It is a bit perplexing that no employees of the hospital developed clinical evidence of influenza, since no program of vaccination had been undertaken among the employees.

Routine vaccination of hospital workers is still controversial, although George et al believe that routine influenza vaccination is necessary among hospital personnel because of the closed hospital environment in which influenza can spread not only to the hospital workers, but from the personnel to the patients.

The severity of the illness in our patients may have been due both to their compromised status and also to their unvaccinated status; and therefore, we believe that routine prophylactic vaccination, as recommended by the Center for Disease Control for compromised patients in the community, should be extended to the high-risk hospitalized patients when documented influenza is present in the community. Other measures might also be considered.

Thus, O’Donoghue et al found that prophylaxis with amantadine resulted in an 89-percent protective effect, and they believe that serious consideration should be given to its use in hospitalized patients during outbreaks of influenza A.

It is intriguing that despite the presence of a susceptible compromised population, the lack of prior vaccination, and the failure to recognize the nature of the epidemic promptly, only a small number of clinical cases occurred. This outbreak may also suggest some change in our thinking about severe infections with influenza virus. It has been widely assumed that if a major epidemic (such as swine influenza) strikes, death in the overwhelming majority of cases will be due to secondary bacterial infection. Our experience raises the possibility that in future epidemics, a greater proportion of deaths than heretofore appreciated may result from the virus itself. This, in turn, might offer additional support for those advocating widespread use of preventive immunization.

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